Uplink sounding for wlan system

ABSTRACT

An access point operates in a wireless local area network. The access point includes one or more memories and a processor, coupled to the one or more memories. The one or more memories include instructions, which when executed by the processor cause the access point to transmit a first frame to a plurality of stations in the wireless network and receive null data packet frames from the plurality of stations. After an interframe space period following the first frame, the instructions cause the access point to generate beamforming information based on the null data packet frames and transmit the beamforming information to the plurality of stations. The first frame indicates to the plurality of stations to each transmit a null data packet frame to the access point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.17/203,568, filed on Mar. 16, 2021, which is a Continuation of U.S.patent application Ser. No. 16/201,996, filed on Nov. 27, 2018, now U.S.Pat. No. 10,992,359, which is a Continuation of U.S. patent applicationSer. No. 15/149,025, filed on May 6, 2016, now U.S. Pat. No. 10,158,413,which claims the benefit of U.S. Provisional Application 62/159,174,filed on May 8, 2015, U.S. Provisional Application No. 62/167,780, filedon May 28, 2015, U.S. Provisional Application 62/245,776, filed on Oct.23, 2015, U.S. Provisional Application 62/250,346, filed on Nov. 3,2015, and U.S. Provisional Application 62/251,594, filed on Nov. 5,2015, the entirety of each of which are incorporated herein by referencefor all purposes.

FIELD OF INVENTION

The present description relates in general to wireless communicationsystems and methods, and more particularly to, for example, withoutlimitation, uplink sounding for wireless local area network (WLAN)systems.

BACKGROUND

Wireless local area network (WLAN) devices are deployed in diverseenvironments. These environments are generally characterized by theexistence of access points and non-access point stations. Increasedinterference from neighboring devices gives rise to performancedegradation. Additionally, WLAN devices are increasingly required tosupport a variety of applications such as video, cloud access, andoffloading. In particular, video traffic is expected to be the dominanttype of traffic in many high efficiency WLAN deployments. With thereal-time requirements of some of these applications, WLAN users demandimproved performance in delivering their applications, includingimproved power consumption for battery-operated devices.

The description provided in the background section should not be assumedto be prior art merely because it is mentioned in or associated with thebackground section. The background section may include information thatdescribes one or more aspects of the subject technology.

SUMMARY

An access point operates in a wireless local area network. The accesspoint includes one or more memories and a processor, coupled top the oneor more memories. The one or more memories include instructions, whichwhen executed by the processor cause the access point to transmit afirst frame to a plurality of stations in the wireless network andreceive null data packet frames from the plurality of stations. After aninterframe space period following the first frame, the instructionscause the access point to generate beamforming information based on thenull data packet frames and transmit the beamforming information to theplurality of stations. The first frame indicates to the plurality ofstations to each transmit a null data packet frame to the access point.

A first station operates in a wireless network. The first stationincludes one or more memories and a processor coupled to the one or morememories. The one or more memories include instructions, which whenexecuted by the processor, cause the first station to receive a triggerframe from an access point that triggers a sounding sequence from a setof stations in the wireless network, transmit a first null data packetframe to the access point as part of a first multi-user uplinktransmission, and receive a multi-user downlink transmission from theaccess point based on the first multi-user uplink transmission. Thefirst multi-user uplink transmission involves the first station and theother stations within the set or stations.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that differentreferences to “an” or “one” embodiment in this specification are notnecessarily to the same embodiment, and such references mean at leastone. Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is submitted that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

FIG. 1 illustrates a schematic diagram of an example of a wirelesscommunication network.

FIG. 2 illustrates a schematic diagram of an example of a wirelesscommunication device.

FIG. 3A illustrates a schematic block diagram of an example of atransmitting signal processor in a wireless communication device.

FIG. 3B illustrates a schematic block diagram of an example of areceiving signal processor in a wireless communication device.

FIG. 4 illustrates an example of a timing diagram of interframe space(IFS) relationships.

FIG. 5 illustrates an example of a timing diagram of a carrier sensemultiple access/collision avoidance (CSMA/CA) based frame transmissionprocedure for avoiding collision between frames in a channel.

FIG. 6 illustrates an example of a high efficiency (HE) frame.

FIG. 7 illustrates an example of a sounding protocol.

FIG. 8 illustrates an example of a non-data packet announcement frame.

FIG. 9 illustrates an example of a beamforming feedback frame.

FIG. 10 illustrates an example of an uplink (UL) sounding protocol.

FIG. 11 illustrates examples of approaches by which to facilitate ULsounding.

FIGS. 12 and 13 illustrate examples of UL sounding protocols.

FIG. 14 illustrates an example of a trigger frame.

FIG. 15-17 illustrate examples of UL sounding protocols.

FIG. 12 is a schematic block diagram exemplifying a transmitting signalprocessor in a WLAN device, according to some embodiments.

FIGS. 18 and 19 illustrate examples of high efficiency long trainingfield (HE-LTF) symbols of a non-data packet frame.

FIG. 20-26 illustrate examples of UL sounding protocols.

FIGS. 27 and 28 illustrate examples of non-data packet frames.

FIGS. 29-31 illustrate examples of numbers of pilots in a 20 MHz, 40MHz, and 80 MHz channel bandwidth numerology, respectively.

FIGS. 32A-32C illustrate flow charts of examples of methods forfacilitating wireless communication for multi-user transmission.

In one or more implementations, not all of the depicted components ineach figure may be required, and one or more implementations may includeadditional components not shown in a figure. Variations in thearrangement and type of the components may be made without departingfrom the scope of the subject disclosure. Additional components,different components, or fewer components may be utilized within thescope of the subject disclosure.

DETAILED DESCRIPTION

The detailed description set forth below is intended as a description ofvarious implementations and is not intended to represent the onlyimplementations in which the subject technology may be practiced. Asthose skilled in the art would realize, the described implementationsmay be modified in various different ways, all without departing fromthe scope of the present disclosure. Accordingly, the drawings anddescription are to be regarded as illustrative in nature and notrestrictive.

In one or more implementations, the subject technology may support anuplink (UL) sounding protocol. The UL sounding protocol may involve abeamformee and one or more beamformers. In a case with more than onebeamformer, the UL sounding protocol may be referred to as a ULmulti-user (MU) sounding protocol. In some aspects, the beamformee maybe an access point (AP), and the beamformers may be stations (e.g.,non-AP stations). In some aspects, the UL MU sounding protocol may beutilized with UL MU transmission technology such as UL MU orthogonalfrequency division multiple access (OFDMA) and/or UL MU multi-inputmulti-output (MIMO). The subject technology may support non-data packet(NDP) sounding, in which NDP frames are utilized in the UL soundingprotocol. The UL sounding protocol may be utilized in high efficiency(HE) WLAN.

The UL sounding protocol may allow one or more beamformers to requestand retrieve beamforming information from a beamformee and compute abeamforming matrix based on beamforming information fed back by thebeamformee to the beamformers. The beamforming information may bereferred to as beamforming report information or beamforming feedbackinformation and may include signal-to-noise ratio (SNR) and/orbeamforming feedback vector/matrix information. The beamformers mayutilize the beamforming information to generate a beamforming matrix andgenerate beamformed data packets (using the beamforming matrix) to betransmitted to the beamformee. When the beamformee is an AP, thebeamformed data packets may contain UL data that is transmitted uplinkto the AP and received by the AP. In some aspects, beamformees maycompress their respective feedback matrices to reduce overheadassociated with the UL sounding protocol. Such feedback matrices may bereferred to as compressed feedback matrices.

In one or more aspects, UL MU operation may allow the beamformee tosolicit (e.g., using a trigger frame) response frames from thebeamformers (e.g., immediate simultaneous response frames from thebeamformers). For simultaneous response frames, the beamformers maytransmit their response frames using UL MU transmission technology(e.g., UL MU OFDMA and/or UL MU-MIMO).

A trigger frame may be a frame sent by an AP that seeks data, control,or management frame response(s) from stations that participate in asubsequent UL MU frame. The trigger frame may be utilized to initiatethe simultaneous MU transmission in OFDMA. In an aspect, a trigger framemay include, for example, some or all of the following features: (a) alist of stations (STAs) that an access point (AP) seeks a response from;(b) resource allocation information for each STA (e.g., a subbandassigned to each STA); and/or (c) attributes of the expected UL MUframe, such as the duration, bandwidth, etc., among other features. Inother words, the trigger frame may be used to allocate resource for ULMU transmission and to solicit an UL MU transmission from theparticipating stations in response to the trigger frame. The term“resource” may refer to, for example, a bandwidth (e.g., a subband(s),frequencies, frequency band(s)), time/duration that the STAs expect tooccupy a transmission medium, and/or possibly a number of spatialstreams that the STAs may use.

The beamforming feedback vector/matrix computed by the beamformee may bereferred to as a beamforming feedback matrix or a feedback matrix forsimplicity. The feedback matrix may be represented as a V matrix. Thebeamforming vector/matrix computed by the beamformer may be referred toas a beamforming matrix for simplicity. The beamforming matrix may alsobe referred to as a steering matrix or pre-coding matrix and may berepresented as a Q matrix. In one aspect, the beamforming matrix andfeedback matrix may change from tone to tone. A tone may be referred toas subcarrier. Each tone may be associated with or otherwise identifiedby a tone index or a subcarrier index. A tone index may be referred toas a subcarrier index.

A sounding protocol may be referred to as a sounding procedure, soundingfeedback sequence, sounding protocol sequence, channel soundingprotocol, channel measurement protocol, channel calibration protocol,channel state information (CSI) sounding protocol, beamforming protocol,channel calibration protocol, or variants thereof (e.g., CSI feedbacksequence).

In one or more implementations, the UL sounding protocol may be utilizedin OFDMA communication. In OFDMA, feedback information (e.g., averageSNR values) in the unit of subband may be helpful. The unit of subbandmay be a portion of a channel bandwidth. In an aspect, the unit ofsubband may include, without limitation, 26 tones, 52 tones, 106 tones,242 tones, and 484 tones. In an aspect, a respective average SNR valuecomputed over each subband may be provided by the beamformee to thebeamformer. In an aspect, when the beamformee is the AP and thebeamformer(s) are the station(s), the AP may allocate subbands to thebeamformer(s) and provide respective feedback information for eachallocated subband to the beamformer(s).

In one or more implementations, the subject technology may providesubband-wise non-data packet announcement (NDPA or NDP-A) schemes andrelevant feedback methods. In some aspects, modifications and/oradditions to the very high throughput (VHT) sounding protocol utilizedin the Institute of Electrical and Electronics Engineers (IEEE) 802.11acstandard may be implemented to facilitate NDP sounding in OFDMAcommunication. In this regard, in some aspects, modifications and/oradditions may be made with respect to NDPA frames and/or feedback reportframes utilized in IEEE 802.11ac.

One or more implementations of the subject technology may allowreduction in the number of NDPA transmissions, reduction in the numberof NDP transmissions, and/or reduction of contention periods betweensounding procedures. One or more aspects of the subject technology mayallow utilizing downlink (DL) OFDMA for an NDPA frame, sending NDPA andNDP frames together, and/or combining a trigger frame with beamforminginformation. In one or more aspects, the subject technology may allowsending feedback in OFDMA. In case of UL MU OFDMA, the UL soundingprotocol may be utilized in HE WLAN.

FIG. 1 illustrates a schematic diagram of an example of a wirelesscommunication network 100. In the wireless communication network 100,such as a wireless local area network (WLAN), a basic service set (BSS)includes a plurality of wireless communication devices (e.g., WLANdevices). In one aspect, a BSS refers to a set of STAs that cancommunicate in synchronization, rather than a concept indicating aparticular area. In the example, the wireless communication network 100includes wireless communication devices 111-115, which may be referredto as stations (STAs).

Each of the wireless communication devices 111-115 may include a mediaaccess control (MAC) layer and a physical (PHY) layer according to anIEEE 802.11 standard. In the example, at least one wirelesscommunication device (e.g., device Ill) is an access point (AP). An APmay be referred to as an AP STA, an AP device, or a central station. Theother wireless communication devices (e.g., devices 112-115) may benon-AP STAs. Alternatively, all of the wireless communication devices111-115 may be non-AP STAs in an Ad-hoc networking environment.

An AP STA and a non-AP STA may be collectively called STAs. However, forsimplicity of description, in some aspects, only a non-AP STA may bereferred to as a STA. An AP may be, for example, a centralizedcontroller, a base station (BS), a node-B, a base transceiver system(BTS), a site controller, a network adapter, a network interface card(NIC), a router, or the like. A non-AP STA (e.g., a client deviceoperable by a user) may be, for example, a device with wirelesscommunication capability, a terminal, a wireless transmit/receive unit(WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal,a mobile subscriber unit, a laptop, a non-mobile computing device (e.g.,a desktop computer with wireless communication capability) or the like.In one or more aspects, a non-AP STA may act as an AP (e.g., a wirelesshotspot).

In one aspect, an AP is a functional entity for providing access to adistribution system, by way of a wireless medium, for an associated STA.For example, an AP may provide access to the internet for one or moreSTAs that are wirelessly and communicatively connected to the AP. InFIG. 1 , wireless communications between non-AP STAs are made by way ofan AP. However, when a direct link is established between non-AP STAs,the STAs can communicate directly with each other (without using an AP).

In one or more implementations, OFDMA-based 802.11 technologies areutilized, and for the sake of brevity, a STA refers to a non-AP highefficiency (HE) STA, and an AP refers to an HE AP. In one or moreaspects, a STA may act as an AP.

FIG. 2 illustrates a schematic diagram of an example of a wirelesscommunication device. The wireless communication device 200 includes abaseband processor 210, a radio frequency (RF) transceiver 220, anantenna unit 230, a memory 240, an input interface unit 250, an outputinterface unit 260, and a bus 270, or subsets and variations thereof.The wireless communication device 200 can be, or can be a part of, anyof the wireless communication devices 111-115.

An HE Control subfield that carries information regarding ROMI isreferred to herein as an HEC-ROMI subfield. An HEC-ROMI subfield maycarry information regarding a change in receiver operation (e.g., interms of bandwidth and/or the number of spatial streams).

In the example, the baseband processor 210 performs baseband signalprocessing, and includes a medium access control (MAC) processor 211 anda PHY processor 215. The memory 240 may store software (such as MACsoftware) including at least some functions of the MAC layer. The memorymay further store an operating system and applications.

In the illustration, the MAC processor 211 includes a MAC softwareprocessing unit 212 and a MAC hardware processing unit 213. The MACsoftware processing unit 212 executes the MAC software to implement somefunctions of the MAC layer, and the MAC hardware processing unit 213 mayimplement remaining functions of the MAC layer as hardware (MAChardware). However, the MAC processor 211 may vary in functionalitydepending on implementation. The PHY processor 215 includes atransmitting (TX) signal processing unit 280 and a receiving (RX) signalprocessing unit 290. The term TX may refer to transmitting, transmit,transmitted, transmitter or the like. The term RX may refer toreceiving, receive, received, receiver or the like.

The PHY processor 215 interfaces to the MAC processor 211 through, amongothers, transmit vector (TXVECTOR) and receive vector (RXVECTOR)parameters. In one or more aspects, the MAC processor 211 generates andprovides TXVECTOR parameters to the PHY processor 215 to supplyper-packet transmit parameters. In one or more aspects, the PHYprocessor 215 generates and provides RXVECTOR parameters to the MACprocessor 211 to inform the MAC processor 211 of the received packetparameters.

In some aspects, the wireless communication device 200 includes aread-only memory (ROM) (not shown) or registers (not shown) that storeinstructions that are needed by one or more of the MAC processor 211,the PHY processor 215 and/or other components of the wirelesscommunication device 200.

In one or more implementations, the wireless communication device 200includes a permanent storage device (not shown) configured as aread-and-write memory device. The permanent storage device may be anon-volatile memory unit that stores instructions even when the wirelesscommunication device 200 is off. The ROM, registers and the permanentstorage device may be part of the baseband processor 210 or be a part ofthe memory 240. Each of the ROM, the permanent storage device, and thememory 240 may be an example of a memory or a computer-readable medium.A memory may be one or more memories.

The memory 240 may be a read-and-write memory, a read-only memory, avolatile memory, a non-volatile memory, or a combination of some or allof the foregoing. The memory 240 may store instructions that one or moreof the MAC processor 211, the PHY processor 215, and/or anothercomponent may need at runtime.

The RF transceiver 220 includes an RF transmitter 221 and an RF receiver222. The input interface unit 250 receives information from a user, andthe output interface unit 260 outputs information to the user. Theantenna unit 230 includes one or more antennas. When multi-inputmulti-output (MIMO) or multi-user MIMO (MU-MIMO) is used, the antennaunit 230 may include more than one antenna.

The bus 270 collectively represents all system, peripheral, and chipsetbuses that communicatively connect the numerous internal components ofthe wireless communication device 200. In one or more implementations,the bus 270 communicatively connects the baseband processor 210 with thememory 240. From the memory 240, the baseband processor 210 may retrieveinstructions to execute and data to process in order to execute theprocesses of the subject disclosure. The baseband processor 210 can be asingle processor, multiple processors, or a multi-core processor indifferent implementations. The baseband processor 210, the memory 240,the input interface unit 250, and the output interface unit 260 maycommunicate with each other via the bus 270.

The bus 270 also connects to the input interface unit 250 and the outputinterface unit 260. The input interface unit 250 enables a user tocommunicate information and select commands to the wirelesscommunication device 200. Input devices that may be used with the inputinterface unit 250 may include any acoustic, speech, visual, touch,tactile and/or sensory input device, e.g., a keyboard, a pointingdevice, a microphone, or a touchscreen.

The output interface unit 260 may enable, for example, the display oroutput of videos, images, audio, and data generated by the wirelesscommunication device 200. Output devices that may be used with theoutput interface unit 260 may include any visual, auditory, tactile,and/or sensory output device, e.g., printers and display devices or anyother device for outputting information. One or more implementations mayinclude devices that function as both input and output devices, such asa touchscreen.

One or more implementations can be realized in part or in whole using acomputer-readable medium. In one aspect, a computer-readable mediumincludes one or more media. In one or more aspects, a computer-readablemedium is a tangible computer-readable medium, a computer-readablestorage medium, a non-transitory computer-readable medium, amachine-readable medium, a memory, or some combination of the foregoing(e.g., a tangible computer-readable storage medium, or a non-transitorymachine-readable storage medium). In one aspect, a computer is amachine. In one aspect, a computer-implemented method is amachine-implemented method.

A computer-readable medium may include storage integrated into aprocessor and/or storage external to a processor. A computer-readablemedium may be a volatile, non-volatile, solid state, optical, magnetic,and/or other suitable storage device, e.g., RAM, ROM, PROM, EPROM, aflash, registers, a hard disk, a removable memory, or a remote storagedevice.

In one aspect, a computer-readable medium comprises instructions storedtherein. In one aspect, a computer-readable medium is encoded withinstructions. In one aspect, instructions are executable by one or moreprocessors (e.g., 210, 211, 212, 213, 215, 280, 290) to perform one ormore operations or a method. Instructions may include, for example,programs, routines, subroutines, data, data structures, objects,sequences, commands, operations, modules, applications, and/orfunctions. Those skilled in the art would recognize how to implement theinstructions.

A processor (e.g., 210, 211, 212, 213, 215, 280, 290) may be coupled toone or more memories (e.g., one or more external memories such as thememory 240, one or more memories internal to the processor, one or moreregisters internal or external to the processor, or one or more remotememories outside of the device 200), for example, via one or more wiredand/or wireless connections. The coupling may be direct or indirect. Inone aspect, a processor includes one or more processors. A processor,including a processing circuitry capable of executing instructions, mayread, write, or access a computer-readable medium. A processor may be,for example, an application specific integrated circuit (ASIC), adigital signal processor (DSP), or a field programmable gate array(FPGA).

In one aspect, a processor (e.g., 210, 211, 212, 213, 215, 280, 290) isconfigured to cause one or more operations of the subject disclosure tooccur. In one aspect, a processor is configured to cause an apparatus(e.g., a wireless communication device 200) to perform operations or amethod of the subject disclosure. In one or more implementations, aprocessor configuration involves having a processor coupled to one ormore memories. A memory may be internal or external to the processor.Instructions may be in a form of software, hardware or a combinationthereof. Software instructions (including data) may be stored in amemory. Hardware instructions may be part of the hardware circuitrycomponents of a processor. When the instructions are executed orprocessed by one or more processors, (e.g., 210, 211, 212, 213, 215,280, 290), the one or more processors cause one or more operations ofthe subject disclosure to occur or cause an apparatus (e.g., a wirelesscommunication device 200) to perform operations or a method of thesubject disclosure.

FIG. 3A illustrates a schematic block diagram of an example of atransmitting signal processing unit 280 in a wireless communicationdevice. The transmitting signal processing unit 280 of the PHY processor215 includes an encoder 281, an interleaver 282, a mapper 283, aninverse Fourier transformer (1FT) 284, and a guard interval (GI)inserter 285.

The encoder 281 encodes input data. For example, the encoder 281 may bea forward error correction (FEC) encoder. The FEC encoder may include abinary convolutional code (BCC) encoder followed by a puncturing device,or may include a low-density parity-check (LDPC) encoder. Theinterleaver 282 interleaves the bits of each stream output from theencoder 281 to change the order of bits. In one aspect, interleaving maybe applied only when BCC encoding is employed. The mapper 283 maps thesequence of bits output from the interleaver 282 into constellationpoints.

When MIMO or MU-MIMO is employed, the transmitting signal processingunit 280 may use multiple instances of the interleaver 282 and multipleinstances of the mapper 283 corresponding to the number of spatialstreams (Nss). In the example, the transmitting signal processing unit280 may further include a stream parser for dividing outputs of the BCCencoders or the LDPC encoder into blocks that are sent to differentinterleavers 282 or mappers 283. The transmitting signal processing unit280 may further include a space-time block code (STBC) encoder forspreading the constellation points from the number of spatial streamsinto a number of space-time streams (NsTs) and a spatial mapper formapping the space-time streams to transmit chains. The spatial mappermay use direct mapping, spatial expansion, or beamforming depending onimplementation. When MU-MIMO is employed, one or more of the blocksbefore reaching the spatial mapper may be provided for each user.

The 1FT 284 converts a block of the constellation points output from themapper 283 or the spatial mapper into a time domain block (e.g., asymbol) by using an inverse discrete Fourier transform (IDFT) or aninverse fast Fourier transform (IFFT). If the STBC encoder and thespatial mapper are employed, the 1FT 284 may be provided for eachtransmit chain.

When MIMO or MU-MIMO is employed, the transmitting signal processingunit 280 may insert cyclic shift diversities (CSDs) to preventunintentional beamforming. The CSD insertion may occur before or afterthe inverse Fourier transform operation. The CSD may be specified pertransmit chain or may be specified per space-time stream. Alternatively,the CSD may be applied as a part of the spatial mapper.

The GI inserter 285 prepends a GI to the symbol. The transmitting signalprocessing unit 280 may optionally perform windowing to smooth edges ofeach symbol after inserting the GI. The RF transmitter 221 converts thesymbols into an RF signal and transmits the RF signal via the antennaunit 230. When MIMO or MU-MIMO is employed, the GI inserter 285 and theRF transmitter 221 may be provided for each transmit chain.

FIG. 3B illustrates a schematic block diagram of an example of areceiving signal processing unit 290 in a wireless communication device.The receiving signal processing unit 290 of the PHY processor 215includes a GI remover 291, a Fourier transformer (FT) 292, a demapper293, a deinterleaver 294, and a decoder 295.

The RF receiver 222 receives an RF signal via the antenna unit 230 andconverts the RF signal into one or more symbols. In some aspects, the GIremover 291 removes the GI from the symbol. When MIMO or MU-MIMO isemployed, the RF receiver 222 and the GI remover 291 may be provided foreach receive chain.

The FT 292 converts the symbol (e.g., the time domain block) into ablock of the constellation points by using a discrete Fourier transform(DFT) or a fast Fourier transform (FFT) depending on implementation. Inone or more implementations, the FT 292 is provided for each receivechain.

When MIMO or MU-MIMO is employed, the receiving signal processing unit290 may further include a spatial demapper for converting the Fouriertransformed receiver chains to constellation points of the space-timestreams, and a STBC decoder (not shown) for despreading theconstellation points from the space-time streams into the spatialstreams.

The demapper 293 demaps the constellation points output from the FT 292or the STBC decoder to the bit streams. If the LDPC encoding is used,the demapper 293 may further perform LDPC tone demapping before theconstellation demapping. The deinterleaver 294 deinterleaves the bits ofeach stream output from the demapper 293. In one or moreimplementations, deinterleaving may be applied only when BCC decoding isused.

When MIMO or MU-MIMO is employed, the receiving signal processing unit290 may use multiple instances on the demapper 293 and multipleinstances of the deinterleaver 294 corresponding to the number ofspatial streams. In the example, the receiving signal processing unit290 may further include a stream deparser for combining the streamsoutput from the deinterleavers 294.

The decoder 295 decodes the streams output from the deinterleaver 294and/or the stream deparser. For example, the decoder 295 may be an FECdecoder. The FEC decoder may include a BCC decoder or an LDPC decoder.

FIG. 4 illustrates an example of a timing diagram of interframe space(IFS) relationships. In this example, a data frame, a control frame, ora management frame can be exchanged between the wireless communicationdevices 111-115 and/or other WLAN devices.

Referring to the timing diagram 400, during the time interval 402,access is deferred while the medium (e.g., a wireless communicationchannel) is busy until a type of IFS duration has elapsed. At timeinterval 404, immediate access is granted when the medium is idle for aduration that is equal to or greater than a distributed coordinationfunction IFS (DIFS) 410 duration or arbitration IFS (AIFS) 414 duration.In turn, a next frame 406 may be transmitted after a type of IFSduration and a contention window 418 have passed. During the time 408,if a DIFS has elapsed since the medium has been idle, a designated slottime 420 is selected and one or more backoff slots 422 are decrementedas long as the medium is idle.

The data frame is used for transmission of data forwarded to a higherlayer. In one or more implementations, a WLAN device transmits the dataframe after performing backoff if DIFS 410 has elapsed from a time whenthe medium has been idle.

The management frame is used for exchanging management information thatis not forwarded to the higher layer. Subtype frames of the managementframe include a beacon frame, an association request/response frame, aprobe request/response frame, and an authentication request/responseframe.

The control frame is used for controlling access to the medium. Subtypeframes of the control frame include a request to send (RTS) frame, aclear to send (CTS) frame, and an ACK frame. In the case that thecontrol frame is not a response frame of the other frame (e.g., aprevious frame), the WLAN device transmits the control frame afterperforming backoff if the DIFS 410 has elapsed. In the case that thecontrol frame is the response frame of the other frame, the WLAN devicetransmits the control frame without performing backoff if a short IFS(SIFS) 412 has elapsed. The type and subtype of frame may be identifiedby a type field and a subtype field in a frame control field of theframe.

On the other hand, a Quality of Service (QoS) STA may transmit the frameafter performing backoff if AIFS 414 for access category (AC), e.g.,AIFS[AC], has elapsed. In this case, the data frame, the managementframe, or the control frame that is not the response frame may use theAIFS[AC].

In one or more implementations, a point coordination function (PCF)enabled AP STA transmits the frame after performing backoff if a PCF IFS(PIFS) 416 has elapsed. In this example, the PIFS 416 duration is lessthan the DIFS 410 but greater than the SIFS 412. In some aspects, thePIFS 416 is determined by incrementing the SIFS 412 duration by adesignated slot time 420.

FIG. 5 illustrates an example of a timing diagram 500 of a carrier sensemultiple access/collision avoidance (CSMA/CA) based frame transmissionprocedure for avoiding collision between frames in a channel. In FIG. 5, anyone of the wireless communication devices 111-115 in FIG. 1 can bedesignated as one of STA1, STA2 or STA3. In this example, the wirelesscommunication device III is designated as STA1, the wirelesscommunication device 112 is designated as STA2, and the wirelesscommunication device 113 is designated as STA3. While the timing of thewireless communication devices 114 and 115 is not shown in FIG. 5 , thetiming of the devices 114 and 115 may be the same as that of STA2.

In this example, STA1 is a transmit WLAN device for transmitting data,STA2 is a receive WLAN device for receiving the data, and STA3 is a WLANdevice that may be located at an area where a frame transmitted from theSTA1 and/or a frame transmitted from the STA2 can be received by theSTA3.

The STA1 may determine whether the channel (or medium) is busy bycarrier sensing. The STA1 may determine the channel occupation based onan energy level on the channel or correlation of signals in the channel.In one or more implementations, the STA1 determines the channeloccupation by using a network allocation vector (NAV) timer.

When determining that the channel is not used by other devices duringthe DIFS 410 (e.g., the channel is idle), the STA1 may transmit an RTSframe 502 to the STA2 after performing backoff. Upon receiving the RTSframe 502, the STA2 may transmit a CTS frame 506 as a response of theCTS frame 506 after the SIFS 412.

When the STA3 receives the RTS frame 502, the STA3 may set a NAV timerfor a transmission duration representing the propagation delay ofsubsequently transmitted frames by using duration information involvedwith the transmission of the RTS frame 502 (e.g., NAV(RTS) 510). Forexample, the STA3 may set the transmission duration expressed as thesummation of a first instance of the SIFS 412, the CTS frame 506duration, a second instance of the SIFS 412, a data frame 504 duration,a third instance of the SIFS 412 and an ACK frame 508 duration

Upon receiving a new frame (not shown) before the NAV timer expires, theSTA3 may update the NAV timer by using duration information included inthe new frame. The STA3 does not attempt to access the channel until theNAV timer expires.

When the STA1 receives the CTS frame 506 from the STA2, the STA1 maytransmit the data frame 504 to the STA2 after the SIFS 412 elapses froma time when the CTS frame 506 has been completely received. Uponsuccessfully receiving the data frame 504, the STA2 may transmit the ACKframe 508 after the SIFS 412 elapses as an acknowledgment of receivingthe data frame 504.

When the NAV timer expires, the STA3 may determine whether the channelis busy by the carrier sensing. Upon determining that the channel is notused by the other WLAN devices (e.g., STA1, STA2) during the DIFS 410after the NAV timer has expired, the STA3 may attempt the channel accessafter a contention window 418 has elapsed. In this example, thecontention window 418 may be based on a random backoff.

FIG. 6 illustrates an example of a high efficiency (HE) frame 600. TheHE frame 600 is a physical layer convergence procedure (PLCP) protocoldata unit (or PPDU) format. An HE frame may be referred to as an OFDMAframe, a PPDU, a PPDU format, an OFDMA PPDU, an MU PPDU, another similarterm, or vice versa. An HE frame may be simply referred to as a framefor convenience. A transmitting station (e.g., AP, non-AP station) maygenerate the HE frame 600 and transmit the HE frame 600 to a receivingstation. The receiving station may receive, detect, and process the HEframe 600. The HE frame 600 may include an L-STF field, an L-LTF field,an L-SIG field, an RL-SIG field, an HE-SIG-A field, an HE-SIG-B field,an HE-STF field, an HE-LTF field, and an HE-DATA field. The HE SIG-Afield may include N_(HESIGA) symbols, the HE-SIG-B field may includeN_(HESIGB) symbols, the HE-LTF field may include N_(HELTF) symbols, andthe HE-DATA field may include N_(DATA) symbols.

In one or more implementations, an AP may transmit a frame for downlink(DL) using a frame format shown in this figure or a variation thereof(e.g., without any or some portions of an HE header). A STA may transmita frame for uplink (UL) using a frame format shown in this figure or avariation thereof (e.g., without any or some portions of an HE header).

Table 1, shown below, provides examples of characteristics associatedwith the various components of the HE frame 600.

DFT Subcarrier Element Definition Duration Period GI Spacing DescriptionLegacy Non-high 8 us — — Equivalent L-STF of a non- (L)-STF throughputto 1.250 trigger-based (HT) Short KHz PPDU has a Training periodicity of0.8 Field us with 10 periods L-LTF Non-HT 8 us 3.2 us 1.6 us 312.5 KHzLong Training Field L-SIG Non-HT 4 us 3.2 us 0.8 us 312.5 KHz SIGNALField RL-SIG Repeated 4 us 3.2 us 0.8 us 312.5 KHz Non-HT SIGNAL FieldHE-SIG- HE N_(HESIGA) * 3.2 us 0.8 us 312.5 KHz HE-SIG-A is A SIGNAL 4us duplicated on each A Field 20 MHz segment after the legacy preambleto indicate HE common control information. N_(HESIGA) means the numberof OFDM symbols of the HE-SIG-A field and is equal to 2 or 4. HE-SIG- HEN_(HESIGB) * 3.2 us 0.8 us 312.5 KHz N_(HESIGB) B SIGNAL 4 us means thenumber of B Field OFDM symbols of the HE-SIG-B field and is variable. DLMU packet contains HE-SIG-B. Single user (SU) packets and UL Triggerbased packets do not contain HE-SIG-B. HE-STF HE Short 4 or 8 us — —Non- HE-STF of a non- Training trigger- trigger-based Field based PPDUhas a PPDU periodicity of 0.8 (equivalent us with 5 periods. to) 1,250 Anon-trigger- KHz based PPDU is not Trigger- sent in response to based atrigger frame. PPDU: The HE-STF of a (equivalent trigger-based to) 625KHz PPDU has a periodicity of 1.6 us with 5 periods. A trigger-basedPPDU is a UL PPDU sent in response to a trigger frame. HE-LTF HE LongN_(HELTF) * 2xLTF: Supports 2xLTF HE PPDU may support Training (DFT 6.4us, 0.8, 1.6, (equivalent 2xLTF mode and 4xLTF Field period + 4xLTF: 3.2us to) 156.25 mode. GI) us 12.8 us KHz, In the 2xLTF mode, 4xLTF: HE-LTFsymbol 78.125 KHz excluding GI is equivalent to modulating every othertone in an OFDM symbol of 12.8 us excluding GI, and then removing thesecond half of the OFDM symbol in time domain. N_(HELTF) means thenumber of HE-LTF symbols and is equal to 1, 2, 4, 6, 8. HE- HE DATAN_(DATA) * 12.8 us  Supports 78.125 KHz  N_(DATA) means the DATA Field(DFT 0.8, 1.6, number of HE data period + 3.2 us symbols GI) us

Referring to FIG. 6 , the HE frame 600 contains a header and a datafield. The header includes a legacy header comprised of the legacy shorttraining field (L-STF), the legacy long training field (L-LTF), and thelegacy signal (L-SIG) field. These legacy fields contain symbols basedon an early design of an IEEE 802.11 specification. Presence of thesesymbols may facilitate compatibility of new designs with the legacydesigns and products. The legacy header may be referred to as a legacypreamble. In one or more aspects, the term header may be referred to asa preamble.

In one or more implementations, the legacy STF, LTF, and SIG symbols aremodulated/carried with FFT size of 64 on a 20 MHz sub-channel and areduplicated every 20 MHz if the frame has a channel bandwidth wider than20 MHz (e.g., 40 MHz, 80 MHz, 160 MHz). Therefore, the legacy field(i.e., the STF, LTF, and SIG fields) occupies the entire channelbandwidth of the frame. The L-STF field may be utilized for packetdetection, automatic gain control (AGC), and coarse frequency-offset(FO) correction. In one aspect, the L-STF field does not utilizefrequency domain processing (e.g., FFT processing) but rather utilizestime domain processing. The L-LTF field may be utilized for channelestimation, fine frequency-offset correction, and symbol timing. In oneor more aspects, the L-SIG field may contain information indicative of adata rate and a length (e.g., in bytes) associated with the HE frame600, which may be utilized by a receiver of the HE frame 600 tocalculate a time duration of a transmission of the HE frame 600.

The header may also include an HE header comprised of an HE-SIG-A fieldand an HE-SIG-B field. The HE header may be referred to as a non-legacyheader. These fields contain symbols that carry control informationassociated with each PLCP service data unit (PSDU) and/or radiofrequency (RF), PHY, and MAC properties of a PPDU In one aspect, theHE-SIG-A field can be carried/modulated using an FFT size of 64 on a 20MHz basis. The HE-SIG-B field can be carried/modulated using an FFT sizeof e.g., 64 or 256 on a 20 MHz basis depending on implementation. TheHE-SIG-A and HE-SIG-B fields may occupy the entire channel bandwidth ofthe frame. In some aspects, the size of the HE-SIG-A field and/or theHE-SIG-B field is variable (e.g., can vary from frame to frame). In anaspect, the HE-SIG-B field is not always present in all frames. Tofacilitate decoding of the HE frame 600 by a receiver, the size of(e.g., number of symbols contained in) the HE-SIG-B field may beindicated in the HE-SIG-A field. In some aspects, the HE header alsoincludes the repeated L-SIG (RL-SIG) field, whose content is the same asthe L-SIG field.

The HE header may further include HE-STF and HE-LTF fields, whichcontain symbols used to perform necessary RF and PHY processing for eachPSDU and/or for the whole PPDU. The HE-LTF symbols may bemodulated/carried with an FFT size of 256 for 20 MHz bandwidth andmodulated over the entire bandwidth of the frame. Thus, the HE-LTF fieldmay occupy the entire channel bandwidth of the frame. In one aspect, theHE-LTF field may occupy less than the entire channel bandwidth. In oneaspect, an HE-LTF sequence may be utilized by a receiver to estimateMIMO channel between the transmitter and the receiver. Channelestimation may be utilized to decode data transmitted and compensate forchannel properties (e.g., effects, distortions). For example, when apreamble is transmitted through a wireless channel, various distortionsmay occur, and a training sequence in the HE-LTF field is useful toreverse the distortion. This may be referred to as equalization. Toaccomplish this, the amount of channel distortion is measured. This maybe referred to as channel estimation. In one aspect, channel estimationis performed using an HE-LTF sequence, and the channel estimation may beapplied to other fields that follow the HE-LTF sequence.

The HE-STF symbols may have a fixed pattern and a fixed duration. Forexample, the HE-STF symbols may have a predetermined repeating pattern.In one aspect, the HE-STF symbols do not require FFT processing. The HEframe 600 may include the data field, represented as HE-DATA, thatcontains data symbols. The data field may also be referred to as apayload field, data, payload or PSDU.

In one or more aspects, additional one or more HE-LTF fields may beincluded in the header. For example, an additional HE-LTF field may belocated after a first HE-LTF field. In one or more implementations, a TXsignal processing unit 280 (or an 1FT 284) illustrated in FIG. 3A maycarry out the modulation described in this paragraph as well as themodulations described in other paragraphs above. In one or moreimplementations, an RX signal processing unit 290 (or an FT 292) mayperform demodulation for a receiver.

In one or more implementations, the subject technology supports soundingprotocols that include non-data packet (NDP) sounding and and/orexplicit feedback from a beamformee to a beamformer. The NDP soundingmay involve the exchanging between the beamformee and beamformer(s) ofnon-data packet announcement (NDPA) frame(s), NDP frame(s), NDPA pollframe(s), NDP poll frames, and/or beamforming report frame(s).

The non-data packet frame may be referred to as a null data packetframe. The non-data packet announcement frame may be referred to as anull data packet announcement frame. A sounding protocol that utilizesNDPA frames and NDP frames may be referred to as an NDP soundingprotocol or NDP-based sounding protocol.

FIG. 7 illustrates an example of a sounding protocol. Although FIG. 7illustrates an example of a sounding protocol with multiple beamformees,the sounding protocol may involve one beamformer and one beamformee insome cases.

The beamformer may initiate the sounding protocol by sending an NDPAframe 710 followed by an NDP frame 712. The NDPA frame 710 may beutilized by the beamformer to identify the beamformees being included bythe beamformer in the sounding protocol and indicate to thesebeamformees that the beamformer requests (e.g., expects) them to prepare(e.g., measure, generate) beamforming information to be fed back to thebeamformer. In an aspect, if the AP is requesting and receivingbeamforming information from the stations, the sounding protocol may bereferred to as a DL sounding protocol.

The NDPA frame 710 may include one or more fields to identify thebeamformees. In some aspects, the NDPA frame 710 may include one StationInformation (STA Info) field for each beamformee. The NDPA frame 710 mayinclude a STA Info 1 field, STA Info 2 field, and STA Info 3 field thatare associated with beamformees 1, 2, and 3, respectively. Each STA Infofield may include an Association Identifier (AID) field that identifiesa respective beamformee. An example of an NDPA frame will be describedfurther below with respect to FIG. 8

The NDPA frame 710 is generally immediately followed by the NDP frame712. Upon receipt of the NDP frame 712, each of the beamformeesidentified in the NDPA frame 710 may generate beamforming information(e.g., average SNR value(s), feedback matrix/matrices) based on the NDPframe 712. In some aspects, the NDP frame 712 may be the HE frame 600,except without the HE-DATA field or with an empty HE-DATA field. Forexample, the NDP frame 712 may include only the header (e.g., the legacyand HE headers) of the HE frame 600. In some aspects, the beamformeesmay compute feedback matrices and/or SNR values based on the NDP frame712. The beamforming information may be based on analysis of, forexample, the training fields (e.g., L-STF, L-LTF, HE-STF, HE-LTF)contained in the NDP frame 712. For example, the beamformees may performmeasurements (e.g., power measurements) on the NDP frame 712 at varioustones.

In response to the NDPA frame 710, beamformee 1 may transmit abeamforming feedback frame 714. The beamforming feedback frame 714includes beamforming information generated by beamformee 1. To retrievethe beamforming information from the remaining beamformees, thebeamformer may transmit a beamforming report poll frame 716, whoseintended recipient may be designated in a Receiver Address (RA) field ofthe beamforming report poll frame 716. The intended recipient of thebeamforming report poll frame 716 is the beamformee whose beamforminginformation is being requested by (e.g., retrieved by) the beamformer.When the beamforming report poll frame 716 identifies beamformee 2 inits RA field, beamformee 2 may transmit a beamforming feedback frame 718to the beamformer in response to the beamforming report poll frame 716.The beamformer may transmit a beamforming report poll frame 720 whose RAfield is designated as beamformee 3. Beamformee 3 may transmit abeamforming feedback frame 722 to the beamformer in response to thebeamforming report poll frame 720. The beamforming feedback frames 718and 722 contain the beamforming information generated by beamformees 2and 3, respectively. An example of a beamforming feedback frame will bedescribed further below with respect to FIG. 9 .

In some aspects, beamformees may compress their respective beamforminginformation (e.g., feedback matrices) to reduce overhead associated withthe sounding protocol. A beamforming feedback frame that containscompressed feedback matrices may be referred to as a compressedbeamforming (CB) feedback frame. The compressed feedback matrices may bereferred to as compressed V matrices and their elements may be referredto as compressed-V beamforming weights. In an aspect, the compressionand/or format of the beamforming information may be indicated by thebeamformer in the NDPA frame. The disclosure may refer to compressedversions of the beamforming information, feedback matrices, and thebeamforming feedback frames for simplicity, although non-compressedversions of the beamforming information, feedback matrices, andbeamforming feedback frames may be utilized.

In an aspect, as shown in FIG. 7 , the beamformer may retrievebeamforming information in the order associated with the index of theSTA Info field. For example, the beamformee associated with STA Info 1field may transmit a beamforming report frame to the beamformer uponreceipt of the NDP frame 712, while the remaining beamformees (e.g.,beamformee 2 and beamformee 3) need to be polled prior to the remainingbeamformees transmitting their respective beamforming report frames tothe beamformer. In this regard, the beamforming report poll frametargets a specific beamformee. The remaining beamformees may be polledsuch that the beamformee associated with the STA Info 2 field is polledand then the beamformee associated with the STA Info 3 field is polled.Other manners by which the beamformer determines an order in whichbeamforming information is retrieved from the beamformees may beutilized.

Upon retrieving the beamforming information from the beamformees, thebeamformer may generate a beamforming matrix to be utilized forgenerating beamformed data packets for beamformees 1, 2, and 3. In oneaspect, the time period between any two adjacent frames 710, 712, 714,716, 718, 720, and 722 may be a short interface space (SIFS). In one ormore implementations, the frames 710, 712, 714, 716, 718, 720, and 722illustrated in FIG. 7 may represent PPDUs. In some aspects, the frames710, 714, 716, 718, 720, and 722 are Media Access Control (MAC) ProtocolData Units (MPDUs) (e.g., MAC frames). The MPDUs may be a payload(s) ofa PPDU The PPDU may have the format of the HE frame 600 shown in FIG. 6.

FIG. 8 illustrates an example of an NDPA frame 800. In some aspects, theNDPA frame 710 of FIG. 7 may be, may include, or may be a part of, theNDPA frame 800. In some aspects, the NDPA frame 800 may be a MAC framethat forms at least a part of the payload of the HE frame 600. The NDPAframe 800 may include a Frame Control field, Duration field, ReceiverAddress (RA) field, Transmitter Address (TA) field, Sounding DialogToken field, Station Information (STA Info) 1 field, STA Info n field,and Frame Check Sequence (FCS) field. It is noted that the ellipsesbetween the STA Info 1 field and STA Info n field indicate that one ormore additional STA Info fields or no STA Info fields are presentbetween the STA Info 1 field and STA Info n field. Each STA Info fieldis associated with one station. Although the NDPA frame 800 includes atleast a STA Info 1 field and a STA Info n field, an NDPA frame mayinclude a single STA Info field.

In some aspects, the TA field may be set to the address of thetransmitter of the NDPA frame 800. In some aspects, when the NDPA frame800 includes more than one STA Info field, the RA field of the NDPAframe 800 may be set to a broadcast address. In some aspects, thebroadcast address may be a MAC sublayer address. The broadcast addressmay be a distinguished, predefined group (e.g., multidestination)address that is utilized to denote a set of all stations on a givennetwork (e.g., LAN). As an example, with reference to FIG. 8 , the TAfield may include the address of the beamformer, and the RA field mayinclude a broadcast address associated with beamformees 1, 2, and 3. Insome aspects (not shown), if an NDPA frame includes a single STA Infofield, the RA field of the NDPA frame may be set to an address (e.g.,MAC address) of the single beamformee associated with the single STAInfo field.

The Sounding Dialog Token field may include reserved bits and a SoundingDialog Token Number field. The Sounding Dialog Token Number field maycontain a value selected by a beamformer to identify an NDPA frame.

Each STA Info field may include an Association Identifier (AID) field, aFeedback Type field, and an Nc Index field. The AID field in each STAInfo field may contain an AID value that identifies a station. Theidentified station may be expected to process an NDP frame that followsthe NDPA frame 800 to prepare sounding feedback based on the NDP frame.An AID field of the STA Info 1, STA Info 2, and STA Info 3 fields may beset to an AID value associated with beamformee 1, 2, and 3,respectively. In some aspects, the AID field may be referred to as theAID12 field, such as in the case that the AID field includes 12 bits(e.g., 12 least significant bits) of the AID value.

The Feedback Type field includes a value indicative of a type offeedback (e.g., SU-feedback, MU feedback) requested by the beamformer.In the MU feedback case, the Nc Index field may be used to indicate thenumber of columns in the compressed beamforming feedback matrix to beprovided by the beamformee to the beamformer. In some aspects, in the SUfeedback case, the Nc Index field is not used. The beamformees maygenerate beamforming information in accordance with the Feedback Typefield and/or the Nc Index field of the NDPA frame 800.

FIG. 9 illustrates an example of a beamforming feedback frame 900. Thebeamforming feedback frame may also be referred to as a beamformingfeedback report frame, beamforming report frame, or report frame. Thebeamforming feedback frame 900 may be a MAC frame. In an aspect, thebeamforming feedback frame 900 may be a payload of the HE frame 600. Thebeamforming feedback frame 900 may be a compressed beamforming feedbackframe (e.g., when beamforming information contained in the beamformingfeedback frame 900 is compressed). The beamforming feedback frame 900may be anyone of beamforming feedback frames 714, 718, and 722.

The beamforming feedback frame 900 includes a Category field, Actionfield, MIMO Control field, Beamforming Report field, and MU ExclusiveBeamforming Report field. In an aspect, the MIMO Control field may beconsidered a header or portion thereof of the beamforming feedback frame900 whereas the Beamforming Report field and the MU ExclusiveBeamforming Report field may be considered a payload or portion thereofof the beamforming feedback frame. The MIMO Control field may containinformation indicative of the format of the Beamforming Report field andthe MU Exclusive Beamforming Report field.

In a non-MU case (e.g., SU case), the beamforming feedback frame doesnot include the MU Exclusive Beamforming Report field. In some aspects,the Beamforming Report field may be referred to as a CompressedBeamforming Report field and used to include compressed beamforminginformation. The Beamforming Report field may contain SU feedbackinformation or MU feedback information depending on the Feedback Typefield of the NDPA frame (e.g., 800 in FIG. 8 ) from the beamformer. Aportion of the Beamforming Report field may include average SNR valuesand another portion of the Beamforming Report field may includebeamforming feedback matrices. The beamformer can calculate abeamforming matrix Q based on the SU and/or MU feedback information.

In an aspect, if the feedback type is SU, the Beamforming Report fieldmay contain the average SNR values over all reported data subcarriers ofspace-time (ST) streams from 1 to Nc. An example of beamforming reportinformation included in the Beamforming Report field is illustrated inTable 2. In this regard, Table 2 provides an example of an order inwhich information is provided in the Beamforming Report field. Forexample, in the Beamforming Report field, an “Average SNR of Space-TimeStream 1” field may be followed by an “Average SNR of Space-Time Stream2” field. In an aspect, Table 2 illustrates VHT compressed beamformingreport information.

TABLE 2 Example of Compressed Beamforming Report information Field Size(bits) Meaning Average SNR of 8 Signal-to-noise ratio at the Space-Timebeamformee for space-time Stream 1 stream 1 averaged over all datasubcarriers. See Table 8-53h (Average SNR of Space-Time Stream isubfield). . . . . . . . . . Average SNR of 8 Signal-to-noise ratio atthe Space-Time beamformee for space-time Stream Nc stream Nc averagedover all data subcarriers. See Table 8-53h (Average SNR of Space-TimeStream i subfield). Compressed Beamforming Na × Compressed beamformingFeedback (b_(ψ) + feedback matrix as defined in Matrix V for subcarrierb_(φ))/2 Table 8-53d (Order of angles in k = scidx(0) the CompressedBeamforming Feedback Matrix subfieid) and Table 8-53e (Quantization ofangles). Compressed Beamforming Na × Compressed beamforming Feedback(b_(ψ) + feedback matrix as defined in Matrix V for subcarrier b_(φ))/2Table 8-53d (Order of angles in k = scidx(1) the Compressed BeamformingFeedback Matrix subfield) and Table 8-53e (Quantization of angles).Compressed Beamforming Na × Compressed beamforming Feedback (b_(ψ) +feedback matrix as defined in Matrix V for subcarrier b_(φ))/2 Table8-53d (Order of angles in k = scidx(2) the Compressed BeamformingFeedback Matrix subfield) and Table 8-53e (Quantization of angles). . .. . . . . . . Compressed Beamforming Na × Compressed beamformingFeedback (b_(ψ) + feedback matrix as defined in Matrix V for subcarrierb_(φ))/2 Table 8-53d (Order of angles in k = scidx(Ns − 1) theCompressed Beamforming Feedback Matrix subfield) and Table 8-53e(Quantization of angles). NOTE scidx( ) is defined in Table 8-53g(Subcarriers for which a Compressed Beamforming Feedback Matrix subfieldis sent back)

In an aspect, if the feedback type is MU, the beamforming feedback frame900 may include additional beamforming report information on top of theinformation provided for SU feedback (e.g., in the Beamforming Reportfield). The additional beamforming report information may include deltaSNR (ΔSNR) for space-time stream from 1 to Nc for each reportedsubcarrier. Table 3 illustrates an example of MU Exclusive BeamformingReport information. In this regard, Table 3 provides an example of anorder in which information is provided in the MU Exclusive BeamformingReport field.

TABLE 3 Example of MU Exclusive Beamforming Report information FieldSize (Bits) Meaning Delta SNR for space-time stream 1 for 4ΔSNR_(sscidx(0), 1) subcarrier k = sscidx(0) . . . . . . . . . Delta SNRfor space-time stream Nc for 4 ΔSNR_(sscidx(0), Nc) subcarrier k =sscidx(0) Delta SNR for space-time stream 1 for 4 ΔSNR_(sscidx(1), 1)subcarrier k = sscidx(1) . . . . . . . . . Delta SNR for space-timestream Nc for 4 ΔSNR_(sscidx(1), Nc) subcarrier k = sscidx(1) . . . . .. . . . Delta SNR for space-time stream 1 for 4ΔSNR_(sscidx(Ns′ − 1), 1) subcarrier k = sscidx(Ns′ − 1) . . . . . . . .. Delta SNR for space-time stream Nc for 4 ΔSNR_(sscidx(1), Nc)subcarrier k = sscidx(Ns′ − 1) NOTE sscidx( ) is defined in Table 8-53j(Number of subcarriers and subcarrier mapping).

In an aspect, an example of the various variables in Table 3 is providedas follows:

ΔSNR _(k,i)=min(max(round(10 log₁₀((∥H _(k) V _(k,i)∥²)/N)−Avg SNR_(i)),−8),−7)

where

k is the subcarrier index in the range of sscidx(O), sscidx(Ns′−1);

i is the space-time stream index in the range of 1, Nc;

Hk is the estimated MIMO channel for subcarrier k;

Vk,_(i) is column i of the beamforming matrix V for subcarrier k;

N is the average noise plus interference power, measured at thebeamformee, that was used to calculate Avg SNR_(i); and

AvgSNR_(i) is the average SNR of space-time stream i reported in theCompressed Beamforming Report information (Average SNR in Space-TimeStream I field).

It is noted that the ellipses in Tables 2 and 3 may indicate that one ormore additional fields or no additional fields are present betweenfields adjacent to the ellipses. In one or more implementations, thesubject technology may support a UL MU sounding protocol to facilitateUL MU transmission (e.g., UL MU OFDMA transmission, UL MU-MIMOtransmission). In some aspects, the UL MU transmission may involvemultiple beamformers (STAs) and a single beamformee (AP). Each of themultiple stations involved in the UL MU transmission may utilize channelinformation obtained from the UL sounding protocol to determine andapply beamforming for its UL MU transmission to the AP. In an aspect,one or more stations may request that a sounding protocol be initiatedbetween the AP and stations. As used herein, for UL MU soundingprotocols, the term beamformers may be used interchangeably withstations (e.g., non-AP stations) and the term beamformee may be usedinterchangeably with an AP.

FIG. 10 illustrates an example of a UL sounding protocol. In FIG. 10 ,the sounding protocol involves one beamformee and two beamformers, wherethe beamformee is an AP and the two beamformers are stations (e.g.,STA1, STA2). The description from FIG. 7 generally applies to FIG. 10 ,with examples of differences between FIG. 7 and FIG. 10 and otherdescription provided herein for purposes of clarity and simplicity.

STA1 may transmit an NDPA frame 1010 followed by an NDP frame 1012 tothe AP to request beamforming information (e.g., UL channel information)associated with a channel between STA1 and the AP. Upon receipt of theNDP frame 1012, the AP may generate beamforming information based on theNDP frame 1012 and transmit to STA1 a beamforming feedback (BF) frame1014 that contains the beamforming information.

Similarly, STA2 may transmit an NDPA frame 1030 followed by an NDP frame1032 to the AP to request beamforming information associated with achannel between STA2 and the AP. Upon receipt of the NDP frame 1032, theAP may generate beamforming information based on the NDP frame 1032 andtransmit to STA2 a beamforming feedback (BF) frame 1034 that containsthe beamforming information. In an aspect, the NDPA frames 1010 and 1030may identify the AP (e.g., in the AID field).

In an aspect, the UL sounding protocol of FIG. 10 may be considered astwo separate UL sounding protocols (e.g., one between STA1 and AP andanother between STA2 and AP). Each of the two UL sounding protocols isassociated with an NDPA frame (e.g., 1010, 1030), an NDP frame (e.g.,1012, 1032), and a beamforming feedback frame (e.g., 1014, 1034). In anaspect, a frame sequence may include, in order, an NDPA frame, an NDPframe, and a beamforming feedback frame, and the frame sequence may bereferred to as a UL sounding frame sequence. Between the two UL soundingframe sequences, there may be contention periods. Furthermore, the ULsounding protocol of FIG. 10 may be associated with more total air-time(e.g., compared to a DL sounding protocol) since there are multiplebeamformers and each beamformer is associated with its own separatesounding frame sequence. In this regard, the NDPA frames 1010 and 1030may be redundant and increase overhead of the UL sounding protocol. Insome cases, due to a clear channel assessment (CCA) time between thesounding frame sequences, the beamforming feedback information may beless coherent regarding an actual channel status relative to a case inwhich the UL sounding protocol is more temporally compact (e.g.,associated with reduced air-time and/or reduced contention periods).

FIG. 11 illustrates examples of approaches by which to facilitate ULsounding. The description from FIG. 10 generally applies to FIG. 11 ,with examples of differences between FIG. 10 and FIG. 11 and otherdescription provided herein for purposes of clarity and simplicity. Asshown in FIG. 11 , in one or more implementations, the subjecttechnology may support efficient sounding protocols for uplink channelsounding. One or more implementations of the subject technology mayfacilitate (1) a reduction in the number of NDPA frames; (2) a reductionin the number of NDP frames; and/or (3) a reduction (e.g., minimization)of contention periods between UL sounding frame sequences.

In one or more implementations, an NDPA frame format associated with aDL sounding protocol may be modified to facilitate a UL soundingprotocol. For instance, with reference back to FIG. 7 , the NDPA frameutilized in a DL sounding protocol may be an announcement from abeamformer to multiple beamformees, and, upon receipt of the NDPA frameby a beamformee, may cause the beamformee to expect to receive an NDPframe from the beamformer. The beamformee may generate beamforminginformation (e.g., channel information) and feed the beamforminginformation back to the beamformer.

To facilitate a UL sounding protocol, in one or more implementations, anNDPA frame may be utilized as an announcement that a beamformee is ready(e.g., expects) to receive NDP frames from one or more beamformers. Inan aspect, such an NDPA frame may be referred to as anNDP-Receiving-Announcement frame. In contrast, the NDPA frame utilizedfor a DL sounding protocol may be referred to as anNDP-Transmitting-Announcement frame. In other words, the AP may transmitan NDP-Receiving-Announcement frame (e.g., in UL sounding) or anNDP-Transmitting-Announcement frame (e.g., in DL sounding) to provide anindication/announcement of an expectation to receive or transmit,respectively, an NDP frame. For simplicity, the term NDPA frame mayrefer to an NDP-Receiving-Announcement frame or anNDP-Transmitting-Announcement frame. In an aspect, with reference toFIG. 8 , one or more bits of the reserved bits in the Sounding DialogToken field of the NDPA frame 800 can be used as an indication ofwhether an NDPA frame is an NDP-Receiving-Announcement frame or anNDP-Transmitting-Announcement frame. In another aspect, one or more bitsof the reserved bits in the Sounding Dialog Token field of the NDPAframe 800 can be used as an indication of whether an NDPA frame is forUL sounding or for DL sounding. In an aspect, other fields of the NDPAframe 800 may be utilized and/or repurposed to include the indication.

FIG. 12 illustrates an example of a UL sounding protocol. Thedescription from FIG. 10 generally applies to FIG. 12 , with examples ofdifferences between FIG. 10 and FIG. 12 and other description providedherein for purposes of clarity and simplicity.

The AP may transmit an NDPA frame 1210 to STA1 and STA2. The NDPA frame1210 may be utilized to identify the beamformers (e.g., STA1, STA2)associated with the UL sounding protocol and may be considered anindication/announcement of the AP being ready to receive NDP frames fromthe stations. In an aspect, since the beamformee transmits the NDPAframe 1210, the beamformee may be considered an initiator of the ULsounding protocol and the beamformers may be considered responders ofthe UL sounding protocol.

In response to the NDPA frame 1210, STA1 may transmit the NDP frame 1012to the AP. The AP may generate beamforming information (e.g., measuredchannel information) based on the NDP frame 1012 and transmit thebeamforming feedback frame 1014 that contains the beamforminginformation (e.g., compressed beamforming information) to STA1.

The AP may transmit an NDP poll frame 1230 to STA2 for requesting thatSTA2 transmit an NDP frame to the AP. In an aspect, the AP may transmitthe NDP poll frame 1230 at an xIFS (e.g., SIFS) after transmitting thebeamforming feedback frame 1014 to STA1. The NDP poll frame 1230 mayidentify an intended recipient of the NDP poll frame 1230 in an RA fieldof the NDP poll frame 1230. In this regard, the NDP poll frame 1230 maytarget a specific beamformer and may be interpreted as anindication/announcement that the AP is ready to receive an NDP framefrom the specific beamformer. The NDP poll frame 1230 may be utilized tocause the beamformer to transmit an NDP frame to the AP.

In response to the NDP poll frame 1230, STA2 may transmit the NDP frame1032 to the AP. The AP may generate beamforming information based on theNDP frame 1032 and transmit the beamforming feedback frame 1034 thatcontains the beamforming information to STA2. In an aspect, another NDPAframe (e.g., NDP-Receiving-Announcement frame) may be utilized in placeof the NDP poll frame 1230. In an aspect, the NDPA frame 1210 and/or theNDP poll frame 1230 may be the NDPA frame 800 or a modified versionthereof.

Referring back to FIG. 8 , in some aspects, to facilitate UL sounding,one or more fields of the NDPA frame 800 of FIG. 8 can besetlinterpreted in a same or similar manner as one or more fields of aVHT NDPA frame whereas other field(s) of the NDPA frame 800 may beset/interpreted differently from the fields of the VHT NDPA frame. In anaspect, the Frame Control, RA, TA, and/or Sounding Dialog Token Numberfields may be the same as in the VHT NDPA frame. In an aspect, the STAInfo field(s) may be interpreted differently from the VHT NDPA frame.For example, for UL sounding, the AID12 field may contain the 12 leastsignificant bits of the AID of a station (e.g., STA1 in FIG. 12 )expected to send an NDP frame (e.g., 1012) that follows an NDPA frame(e.g., 1210) or an NDP poll frame (e.g., 1230). In some cases, the AID12field may be set equal to 0 if the station is an AP, mesh station, orstation that is a member of an independent basic service set (MSS). TheFeedback Type field may indicate the type of feedback to be sent (e.g.,by the beamformee to the beamformer). In some cases, the Feedback Typefield can be set to single user (SU). The Nc Index field may be the sameas in the VHT NDPA frame. In some cases, the Nc Index field can bereserved since the feedback is SU.

In one or more implementations, a UL MU trigger frame may be utilized toreduce the number of NDP transmissions. In an aspect, the UL MU triggerframe may be utilized to trigger NDP transmission in a UL MU OFDMAand/or UL MU-MIMO manner. In such an aspect, the UL MU trigger frame maybe referred to as an NDP trigger frame. The UL MU trigger frame mayinclude station information that identifies the stations associated withthe UL MU sounding protocol. In an aspect, for each station associatedwith the UL MU sounding protocol, the station information may indicatethe station's AID or partial AID (e.g., AID12) and a number of streamsfor the station. The UL MU trigger frame may include resource allocationinformation for NDP transmission. For instance, the resource allocationinformation may indicate which frequency/spatial resource(s) areallocated to which stations for transmission of NDP frames by thestations (e.g., the beamformers) to the AP (e.g., the beamformee).

In some aspects, the UL MU trigger frame may include a maximum rankvalue among the stations. The maximum rank value may be, or may beindicative of, a highest number of spatial steams utilized by one of thestations. In an aspect, the number of HE-LTF symbols included in an NDPframe for all the stations may be based on (e.g., proportional to) themaximum rank value, as described below with respect to FIGS. 18 and 19 .The maximum rank value may be utilized by all the stations to allow thestations to be aligned in terms of HE-LTF symbols (e.g., utilize thesame number of HE-LTF symbols).

FIG. 13 illustrates an example of a UL sounding protocol. In FIG. 13 ,the AP (e.g., the beamformee) may transmit a trigger frame 1310 tosolicit an NDP frame from the stations (e.g., STA1, STA2) associatedwith the sounding protocol. In an aspect, the trigger frame 1310 may bereferred to as a UL MU trigger frame, an NDP trigger frame, an NDPtriggering frame, or a variant thereof (e.g., a UL NDP trigger frame).In an aspect, the trigger frame 1310 may be utilized by the AP tosolicit an NDP frame simultaneously from the beamformers. For instance,the NDP frames 1012 and 1032 of the beamformers may be multiplexed by ULMU OFDMA and/or UL MU-MIMO.

In some aspects, the trigger frame 1310 may indicate resource allocationinformation for the beamformers, including but not limited to afrequency subband (or a frequency subchannel) assigned to eachrespective one of the beamformers. In some aspects, the resourceallocation information may also include scheduling information regardingwhen a respective one of the beamformers may transmit using its assignedfrequency subband, and/or may include the number of spatial streams thatthe beamformers may use. In response to the trigger frame 1310, STA1 andSTA2 may transmit (e.g., simultaneously transmit) the NDP frame 1012 and1032, respectively. In an aspect, the NDP frames 1012 and 1032 may betransmitted in a UL MU OFDMA and/or UL MU-MIMO manner in accordance withthe resource allocation information of the trigger frame 1310. Forinstance, STA1 and STA2 may transmit the NDP frame 1012 and 1032,respectively, in a respective frequency subband assigned to STA1 andSTA2.

Upon receipt of the NDP frames 1012 and 1032, the AP may generaterespective beamforming information based on each of the NDP frames 1012and 1032. The AP may transmit to STA1 the beamforming feedback frame1014 that contains the beamforming information generated based on theNDP frame 1012 and transmit to STA2 the beamforming feedback frame 1034that contains the beamforming information generated based on the NDPframe 1032. In an aspect, the beamforming information generated based onthe NDP frames 1012 and 1032 may be associated with the respectivefrequency subband(s) in which the NDP frames 1012 and 1032 weretransmitted. For instance, if the NDP frame 1012 is transmitted in afrequency subband, the beamforming information generated based on theNDP frame 1012 may be applicable to beamforming for the frequencysubband.

In an aspect, the beamforming feedback frames 1014 and 1034 may betransmitted sequentially in time. For instance, the AP may transmit thebeamforming feedback frame 1014 to STA1 followed by the beamformingfeedback frame 1034 to STA2. In another aspect, the AP may transmit thebeamforming feedback frames 1014 and 1034 simultaneously in time, witheach beamforming feedback frame being multiplexed in DL MU (e.g., MUOFDMA, MU-MIMO). In an aspect, the resources utilized for DL MU may bethe same as the resources utilized for UL MU For instance, the AP maytransmit the beamforming feedback frames 1014 and 1034 to STA1 and STA2,respectively, in the same frequency subbands as those allocated to STA1and STA2 for the NDP frame transmission.

In some aspects, the frames 1014, 1034, and 1310 are Media AccessControl (MAC) Protocol Data Units (MPDUs) (e.g., MAC frames). The MPDUsmay be a payload(s) of a PPDU multiplexed by UL OFDMA and/or UL MU-MIMO.For instance, the frames 1014 and 1034 may be payloads of a PPDU 1360.The frames 1012 and 1032 may be a part of a PPDU 1350. For instance,HE-LTF field(s) of the NDP frames 1012 and 1032 may be multiplexed by ULOFDMA. The PPDUs 1350 and 1360 may have the format of the HE frame 600shown in FIG. 6 .

In one or more aspects, the trigger frame 1310 can have an indication ofwhether or not the trigger frame 1310 is for soliciting NDP frames fromthe beamformers. The indication (e.g., indication bit or bits) may bereferred to as an explicit indication. In some aspects, the triggerframe 1310 does not include an explicit indication. In such aspects, thebeamformers may implicitly determine whether or not the trigger frame1310 is for soliciting NDP frames based on a length contained in thetrigger frame 1310. The length contained in the trigger frame 1310 maybe indicative of a length of a UL MU PPDU to be transmitted by thebeamformers in response to the trigger frame 1310 and may be referred toas a PPDU length, a UL PPDU length, a following UL PPDU length, a UL MUPPDU length, or a variant thereof.

Since NDP frames (which contain no HE-DATA field) generally have a shortPPDU length, a beamformer that receives the trigger frame 1310 mayparse/decode the payload of the trigger frame 1310 to obtain the PPDUlength and determine whether or not the trigger frame 1310 is forsoliciting NDP frames. For instance, the beamformer may determine thatthe trigger frame 1310 is for soliciting NDP frames when the lengthindicated by trigger frame 1310 is a shortest possible PPDU length or alength less than a predetermined threshold length. With reference toFIG. 13 , the UL MU PPDU solicited by the trigger frame 1310 may includethe NDP frames 1012 and 1032 from STA1 and STA2, respectively.

In an aspect, the location of information bites) in the trigger frame1310 that contain the UL MU PPDU length may be such that the UL MU PPDUlength may be decodable first. In an aspect, within a specific frequencyband allocation for MU NDP frame transmission, MU-MIMO can also beapplied. For example, the trigger frame 1310 may allocate a resourceunit (e.g., RU #4) to multiple stations and these stations allocated tothe resource unit may be multiplexed in the spatial domain. In thisexample, the trigger frame 1310 may also include spatial configurationinformation, such as a start and end index among total spatial streamsfor each station.

FIG. 14 illustrates an example of a trigger frame 1400. In some aspects,the trigger frame 1310 of FIG. 13 may be, may include, or may be a partof, the trigger frame 1400. The trigger frame 1400 includes a FrameControl (FC), a Duration, a Common Information (Common Info), Per UserInformation (Per User Info), and a Frame Check Sequence (FCS) field,among other fields. In an aspect, the station information (e.g., AID,number of spatial streams) and resource allocation information (e.g.,frequency resource allocation information) can be included in the CommonInfo field and/or the Per User Info field(s). In an aspect, the maximumrank value among stations may be included in the Common Info field,since the maximum rank value may affect a number of HE-LTF symbols to beincluded in an NDP frame for all stations. In another aspect, themaximum rank value may be included in a TBD field such as an Al field.The Al field may be an RA field that may be repurposed to contain otherinformation, such as to contain the maximum rank value.

In one or more aspects, the trigger frame 1400 may be an NDPA frame(e.g., 800) or a modified version thereof, such as anNDP-Receiving-Announcement frame. In such aspects, the NDPA frame (e.g.,in the STA Info field) may include resource allocation information foreach station.

FIG. 15 illustrates an example of a UL sounding protocol. Thedescription from FIG. 13 generally applies to FIG. 15 , with examples ofdifferences between FIG. 13 and FIG. 15 and other description providedherein for purposes of clarity and simplicity. In FIG. 15 , the AP maytransmit an NDPA frame 1510 to solicit an NDP frame from the stations(e.g., STA1, STA2) associated with the UL sounding protocol. The NDPAframe 1510 may indicate resource allocation information for the stationsand, when received by the stations, may cause each station to transmit(e.g., simultaneously transmit) an NDP frame using resources indicatedto the station in the NDPA frame 1510. The stations may transmit the NDPframes 1012 and 1032 in an UL MU OFDMA and/or UL MU-MIMO manner. Uponreceipt of the NDP frames 1012 and 1032, the AP may generate respectivebeamforming information based on each of the NDP frames 1012 and 1032and transmit (e.g., simultaneously transmit or sequentially transmit)the beamforming feedback frames 1014 and 1034 that contain therespective beamforming information.

In one or more implementations, a station can request an AP to initiatea UL sounding protocol that includes the requesting station. In anaspect, the request may be a request bit included in an HE controlfield, a quality of service (QoS) control field, or any reserved fieldin a MAC header of a UL frame transmitted to the AP prior to the APinitiating UL sounding. In some cases, even without thisrequest/indication from the station, the AP can determine whether asounding protocol should be initiated for updating UL channel stateinformation (CSI) since triggering for UL MU transmission from stationsand scheduling of the UL MU transmission may be performed/determined bythe AP. However, in some cases, a station may be more aware than the APof when some updates to the station's UL CSI is desirable, and thus theAP may trigger and/or schedule the sounding protocol based at least inpart on the station's request.

In some aspects, when a station requests that the AP initiate ULsounding, the station may provide the AP with additional informationsuch as, for instance, a buffer status report of the station and apreferred bandwidth information (e.g., a preferred subband or a set ofpreferred subbands) for which the station requests to receivebeamforming feedback information. Based on the request and additionalinformation, the AP can initiate a UL sounding protocol. In an aspect,more than one station may request the AP to initiate the UL soundingprotocol.

The AP may determine whether to trigger and schedule a UL soundingprotocol based on information (if any) provided by the station(s) (e.g.,the preferred subband(s) included with a request), although, in someaspects, the AP can determine whether to trigger and schedule the ULsounding protocol at its sole discretion and does not need to take intoconsideration information from the station(s). Similarly, the AP mayallocate resources (e.g., frequency subbands) to the stations based oninformation (if any) provided by the station(s), although, in someaspects, the AP can allocate the resources at its sole discretion anddoes not need to take into consideration information from thestation(s).

FIG. 16 illustrates an example of a UL sounding protocol. Thedescription from FIG. 13 generally applies to FIG. 16 , with examples ofdifferences between FIG. 13 and FIG. 16 and other description providedherein for purposes of clarity and simplicity.

STA1 and STA2 may transmit an uplink frame 1642 and 1644, respectively,that each contains a UL sounding request. In an aspect, the uplinkframes 1642 and 1644 may include preferred bandwidth information and/ora buffer status report associated with STA1 and STA2, respectively. TheAP may transmit the NDPA frame 1510 to solicit NDP frames. In an aspect,the AP may, but need not, transmit the NDPA frame 1510 in response tothe uplink frames 1642 and 1644. The AP may transmit the NDPA frame 1510to solicit NDP frames from stations from which the AP has received a ULsounding request and/or from a station(s) from which the AP has notreceived a UL sounding request. In FIG. 16 , for instance, the AP maytransmit the NDPA frame 1510 to solicit NDP frames from STA3 in additionto STA1 and STA2. In an aspect, NDPA frame 1510 may be a trigger frame(e.g., 1310). It is noted that contentions may occur during a timeduration 1640 prior to transmission of the NDPA frame 1510.

In response to the NDPA frame 1510, STA1 may transmit the NDP frame1012, STA2 may transmit the NDP frame 1032, and STA3 may transmit an NDPframe 1646. The NDP frames 1012, 1032, and 1646 may be transmitted in ULOFDMA and/or UL MU-MIMO manner as part of the PPDU 1350. Upon receipt ofthe NDP frames 1012, 1032, and 1646, the AP may generate respectivebeamforming information based on each of the NDP frames 1012, 1032, and1646. In this regard, the AP may transmit the beamforming feedbackframes 1014, 1034, and 1648 that contain the beamforming informationgenerated based on the NDP frames 1012, 1032, and 1646, respectively.

In one or more implementations, upon receipt of a trigger frame by astation, the station may determine whether or not the trigger frame issoliciting an NDP frame from the station. The station may make thedetermination based on explicit and/or implicit information associatedwith the trigger frame. For instance, the station may determine whetheror not the trigger frame is for soliciting an NDP frame based at leastin part on a UL MU PPDU length contained in the trigger frame. In anaspect, when the station determines that the trigger frame is forsoliciting an NDP frame, the station shall transmit an NDP frame to theAP regardless of any other conditions (e.g., regardless of CCA checkresults and existence of any other frame to be sent by the station oranother station), as shown FIG. 17 .

FIG. 17 illustrates an example of a UL sounding protocol. In someaspects, the trigger frame 1310 may include a shortest possible UL PPDUlength or a length less than a predetermined threshold length (e.g., toallow STA1 and STA2 to determine that the trigger frame 1310 is forsoliciting NDP frames). STA1 and STA2 may transmit the NDP frames 1012and 1032 in the resource(s) specified in the trigger frame 1310. In someaspects, the AP may provide STA1 and/or STA2 with an indication ofwhether or not to perform CCA.

In some aspects, upon receiving the trigger frame 1310 from the AP, STA1and STA2 may transmit the NDP frames 1012 and 1032 after the triggerframe 1310 regardless of CCA check results and existence of any otherframe to be sent after the trigger frame 1310, such as a framepreviously scheduled to be sent between the end of the trigger frame1310 and the end of the time block 1705. In these aspects, a station'sbehavior may be different from the station behavior associated with anon-HE trigger frame (e.g., IEEE 802.11ac-based trigger frame). In anaspect, in the non-HE case, a triggered station may determine (e.g.,based on criteria associated with CCA check results and/or existence ofany other frame to be sent after the trigger frame) not to send a framein response to a trigger frame.

In other aspects, transmission of the NDP frames 1012 and 1032 may beset to be dependent (e.g., optionally dependent) on CCA check results.In these aspects, STA1 and STA2 may take CCA check results intoconsideration when determining whether or not to transmit the NDP frames1012 and 1032, respectively. In an aspect, the CCA check may beperformed during an interframe spacing interval before transmission ofthe NDP frames 1012 and 1032.

In one or more implementations, after receiving an NDP trigger frame,each station may transmit an NDP frame in an allocated frequency band.In an aspect, the NDP frame from each station may be transmitted inaccordance with one or more of the following:

-   -   HE-LTF sequence for each subband allocated to a station is sent        by the station to the AP;    -   The number of HE-LTF symbols corresponds to the maximum rank        value among STAs and is set to be the same for all stations;    -   None of the stations send an NDP frame (e.g., HE-LTF symbols of        the NDP frame) in non-allocated subbands.

FIG. 18 illustrates an example of HE-LTF symbols of an NDP frame. InFIG. 18 , STA1 and STA2 transmit the HE-LTF symbols of the NDP frame ina respective subband allocated to STA1 and STA2. In an aspect, thenumber of HE-LTF symbols transmitted by STA1 and STA2 are the same. Insome aspects, the AP may determine the number of HE-LTF symbols to betransmitted by both STA1 and STA2 based on a higher number of spatialstreams between STA1 and STA2 and may indicate this number to STA1 andSTA2 (e.g., in a trigger frame). For instance, at the time ofassociation, the AP may obtain the maximum number of antennas/spatialstreams that each station may support. The obtained information may thenbe utilized by the AP when determining the number of HE-LTF symbols tobe transmitted by STA1 and STA2.

The subbands allocated to STA1 and STA2 are within an operatingbandwidth associated with UL transmission. In an aspect, the operatingbandwidth may be 20 MHz, 40 MHz, 80 MHz, or 160 MHz, and the subbandsallocated to each station may be a portion of the operating bandwidth.In an aspect, the NDP frame may be the HE frame 600 without the HE-DATAfield. The legacy header and the non-legacy header (e.g., HE header)excluding the HE-LTF symbols may be transmitted over the entireoperating bandwidth, whereas the HE-LTF symbols may be transmitted inthe subbands allocated to the stations. Examples of the NDP frame aredescribed below with respect to FIGS. 27 and 28 . In an aspect, noHE-LTF transmission occurs within a subband of the operating bandwidthto which no station is allocated.

FIG. 19 illustrates an example of HE-LTF symbols of an NDP frame. Thedescription from FIG. 18 generally applies to FIG. 19 , with examples ofdifferences between FIG. 18 and FIG. 19 and other description providedherein for purposes of clarity and simplicity. In FIG. 19 , the subbandsallocated to STA2 and STA4 overlap. The HE-LTF symbols of STA2 and STA4may be multiplexed in the spatial domain (e.g., in UL MU-MIMO manner).

In one or more implementations, the NDP trigger frame (e.g., 1310) maybe used for downlink beamforming with implicit sounding mechanism. Inthe implicit sounding mechanism, the beamformer can utilize CSI forreceived signals to facilitate its transmit signal beamforming.

FIG. 20 illustrates an example of a UL sounding protocol. Thedescription from FIG. 13 generally applies to FIG. 20 , with examples ofdifferences between FIG. 13 and FIG. 20 and other description providedherein for purposes of clarity and simplicity. After the AP transmitsthe trigger frame 1310 and receives the NDP frames 1012 and 1032 (e.g.,as a part of the UL MU PPDU 1350) from corresponding stations, the APdoes not send a beamforming feedback frame to the stations. The AP mayutilize uplink channel information collected or determined based on theNDP frames 1012 and 1032 for applying a subsequent downlink sounding(not shown). Such a UL sounding protocol may be referred to as an NDPtrigger with no compressed beamforming (CB). In an aspect, the triggerframe 1310 may include an indication that no beamforming feedback frameto the stations (e.g., STA1 and STA2) follows in response to the NDPframes (e.g., 1012 and 1032) transmitted by the stations (e.g., STA1 andSTA2) to the AP. In an aspect, the NDP frames 1012 and 1032 can bemultiplexed in spatial domain, along with OFDMA multiplexing.

In one or more implementations, the subject technology facilitates areduction in contention periods in the UL sounding protocol. Forinstance, the subject technology may provide a reduction in contentionperiods between sounding frame sequences associated with differentstations. In some aspects, the subject technology may provide a soundingprotocol that combines multiple NDP sounding frame sequences by usingxIFS (e.g., SIFS) and NDPA (or NDP) poll frames.

FIG. 21 illustrates an example of a UL sounding protocol. Thedescription from FIGS. 10 and 12 generally apply to FIG. 21 , withexamples of differences and other description provided herein forpurposes of clarity and simplicity.

STA1 may transmit the NDPA frame 1010 followed by the NDP frame 1012.The AP may generate beamforming information based on the NDP frame 1012and transmit the beamforming feedback frame 1014. The AP may transmit anNDPA poll frame 2178 for requesting that STA2 transmit an NDPA frame tothe AP. In an aspect, the AP may transmit the NDPA poll frame 2178 at anxIFS (e.g., SIFS) after transmission of the beamforming feedback frame1014 to STA1. In another aspect, the AP may transmit (e.g.,simultaneously transmit) the beamforming feedback frame 1014 and theNDPA poll frame 2178 in an MU OFDMA and/or MU-MIMO manner. In such anaspect, the beamforming feedback frame 1014 and the NDPA poll frame 2178may be part of (e.g., payload(s) of) a PPDU 2170. In response to theNDPA poll frame 2178, STA2 may transmit the NDPA frame 1030 followed bythe NDP frame 1032 to the AP. Upon receipt of the NDP frame 1032, the APmay generate beamforming information based on the NDP frame 1032 andtransmit to STA2 a beamforming feedback frame 1034 that includes thebeamforming information.

FIG. 22 illustrates an example of a UL sounding protocol. Thedescription from FIGS. 10 and 12 generally apply to FIG. 21 , withexamples of differences and other description provided herein forpurposes of clarity and simplicity.

The AP may transmit the NDPA frame 1210 to STA1 and STA2. In response tothe NDPA frame 1210, STA1 may transmit the NDP frame 1012 to the AP. TheAP may generate beamforming information based on the NDP frame 1012 andtransmit the beamforming feedback frame 1014 that contains thebeamforming information to STA1. The AP may transmit the NDP poll frame1230. In an aspect, the AP may transmit the NDP poll frame 1230 after orsimultaneously with (e.g., MU OFDMA and/or MU-MIMO) the beamformingfeedback frame 1014. In response to the NDP poll frame 1230, STA2 maytransmit the NDP frame 1032 to the AP. The AP may generate beamforminginformation based on the NDP frame 1032 and transmit the beamformingfeedback frame 1034 that contains the beamforming information to STA2.

In FIGS. 21 and 22 , in cases in which additional stations areassociated with the UL sounding protocol, the AP may transmit an NDPApoll frame (in FIG. 21 ) or an NDP poll frame (in FIG. 22 ) to a nextstation (e.g., STA3) after or simultaneously with (e.g., MU OFDMA and/orMU-MIMO) the beamforming feedback frame 1034.

FIG. 23 illustrates an example of a UL sounding protocol. Thedescription from FIG. 13 generally applies to FIG. 23 , with examples ofdifferences between FIG. 13 and FIG. 23 and other description providedherein for purposes of clarity and simplicity.

In FIG. 23 , the AP may transmit NDPA frames 2382 and 2384. The NDPAframes 2382 and 2384 may be NDP-Receiving-Announcement frames. The NDPAframes 2382 and 2384 can be multiplexed and transmitted in DL OFDMA as apart of a PPDU 2386 to STA1 and STA2. In response to the NDPA frames2382 and 2384, STA1 and STA2 may transmit the NDP frames 1012 and 1032,respectively, to the AP. Each of the NDPA frames 2382 and 2384 may havea single STA Info field. The respective STA Info field of the NDPAframes 2382 and 2384 may be associated with STA1 and STA2, respectively.In an aspect, each station transmits its NDP frame in the subbands inwhich the respective NDPA frame is received on. For instance, if theNDPA frame 2382 is associated with STA1, STA1 may transmit the NDP frame1012 using the same subband in which STA1 received the NDPA frame 2382.The NDP frames 1012 and 1032 sent by the stations can be multiplexed inUL MU-MIMO alternative to or in addition to UL MU OFDMA. In the case ofmultiplexing in UL MU-MIMO, each NDPA frame or STA information for aspecific station (e.g., STA Info shown in FIG. 8 ) may include thenumber of streams and stream offset to allow each of the stations todetermine its absolute stream index when the stations send NDP framesusing UL MU-MIMO multiplexing.

FIG. 24 illustrates an example of a UL sounding protocol. Thedescription from FIG. 13 generally applies to FIG. 24 , with examples ofdifferences between FIG. 13 and FIG. 24 and other description providedherein for purposes of clarity and simplicity.

In FIG. 24 , after the AP triggers UL MU transmission using the triggerframe 1310, each station can transmit an NDPA frame and an NDP frame.STA1 may transmit an NDPA frame 2482 followed by the NDP frame 1012 andSTA2 may transmit an NDPA frame 2484 followed by the NDP frame 1032. Inan aspect, each station may transmit the respective NDPA frame and NDPframe in the subbands allocated to the station by the trigger frame1310. The NDPA frames 2482 and 2484 can be multiplexed as a UL MU OFDMAPPDU 2486. The NDP frames 1012 and 1032 can be multiplexed as the PPDU1350 (e.g., UL MU OFDMA PPDU). An xIFS (e.g., SIFS, PIFS) may be betweenthe PPDUs 2486 and 1350.

In one or more implementations, a UL MU trigger frame may includefeedback information associated with a UL sounding protocol. In anaspect, the UL MU trigger frame may include compressed or uncompressedbeamforming information (e.g., uplink measurement reports) for multiplestations.

FIG. 25 illustrates an example of a UL sounding protocol. In response toreceiving the NDP frames 1012 and 1032, the AP may generate beamforminginformation based on the NDP frames 1012 and 1032. The AP may thentransmit a trigger frame 2588 to allow UL MU transmission of data. Thetrigger frame 2588 may contain the beamforming information generatedbased on the NDP frames 1012 and 1032. Although the NDP frames 1012 and1032 are illustrated as being transmitted simultaneously, the NDP frames1012 and 1032 may be transmitted sequentially in time. Since the ULsounding protocol is generally linked to and generally precedes a UL MUtransmission, utilizing the trigger frame 2588 that triggers the UL MUtransmission and contains information to facilitate UL beamforming mayhelp reduce overhead associated with UL sounding. In an aspect, an NDPAand NDP Tx/Rx block 2589 of FIG. 25 may represent sounding framesequences (including one or more frames) that precede transmission ofbeamforming feedback frames in, for example, any one of FIGS. 10-13,15-17 , and 20-24.

FIG. 26 illustrates an example of a UL sounding protocol. Thedescription from FIG. 25 generally applies to FIG. 26 , with examples ofdifferences between FIG. 25 and FIG. 26 and other description providedherein for purposes of clarity and simplicity. In an aspect, the ULsounding protocol of FIG. 26 provides an example of the NDPA and NDPTx/Rx block 2589 and an example of frame transmission subsequent to thetrigger frame 2588 of FIG. 25 .

The AP may transmit the NDPA frame 1210. The NDPA frame 1210 may be anNDP trigger frame. In response to the NDPA frame 1210, STA1 and STA2 maytransmit the NDP frames 1012 and 1032, respectively (e.g., multiplexedin UL OFDMA and/or MU-MIMO). The AP may transmit the trigger frame 2588.In response to receiving the trigger frame 2588, STA1 and STA2 maytransmit uplink frames 2590 and 2592, each of which contains data (e.g.,MU data). In an aspect, the uplink frames 2590 and 2592 may bebeamformed based on the beamforming information provided in the triggerframe 2588. In an aspect, the uplink frames 2590 and 2592 may betransmitted simultaneously by their respective station based on resourceallocation information included in the trigger frame 2588. For instance,the uplink frames 2590 and 2592 may be multiplexed by UL MU OFDMA and/orUL MU-MIMO, such as in a PPDU 2594.

In an aspect, the AP may utilize the NDPA frame 1210 to collectinformation (e.g., channel state information, buffer status information,etc.) from the stations. After receiving MU NDP frames from thestations, the AP may transmit the trigger frame 2588 (which containsbeamforming information to allow beamforming by the stations) to receiveUL MU data from the stations. In an aspect, the information collected bythe AP may be utilized by the AP to schedule sending of a trigger frameto cause UL MU transmission and/or determine resource allocationinformation for each station.

In one or more implementations, each station may utilize an NDPtransmission (or lack of an NDP transmission) to implicitly indicatewhether or not the station has data to send. The AP may send an NDPtrigger frame (e.g., 1310) to the stations, where the NDP trigger framecontains resource allocation information for the stations. In an aspect,a station that receives the NDP trigger frame and has a UL data to sendmay send an NDP frame (e.g., 1012) using the resources assigned to thestation in the NDP trigger frame. In an aspect, a station that receivesthe NDP trigger frame but does not have any UL data to send does notsend an NDP frame in response to receiving the NDP trigger frame. The APmay determine whether or not a station has sent an NDP frame based on adetection mechanism algorithm (e.g., energy detection of assignedresources). The AP may interpret that a station does not have UL data tosend if no NDP frame was received from the station.

In one or more implementations, an NDP frame format may be provided tofacilitate collection of information (e.g., bit-wise information) suchas buffer status information from stations. FIG. 27 illustrates anexample of an NDP frame 2700. The description from FIG. 6 generallyapplies to FIG. 27 , with examples of differences between FIG. 6 andFIG. 27 and other description provided herein for purposes of clarityand simplicity. The NDP frame 2700 may include an L-STF field, an L-LTFfield, an L-SIG field, an RL-SIG field, an HE-SIG-A field, an HE-STFfield, and an HE-LTF field(s). In an aspect, the AP may measure the ULchannel through the HE-LTF symbols. The HE-LTF symbols may be associatedwith frequency/spatial multiplexing based on resource allocationinformation in a trigger frame (e.g., an NDP trigger frame). In anaspect, an HE-RSIG-A (HE-Repeated-SIG-A) field can be located betweenthe HE-SIG-A field and HE-STF field for coverage extension.

FIG. 28 illustrates an example of an NDP frame 2800. The descriptionfrom FIG. 27 generally applies to FIG. 28 , with examples of differencesbetween FIG. 27 and FIG. 28 and other description provided herein forpurposes of clarity and simplicity. The NDP frame 2800 includes aSignature field that contains a signature symbol(s). The signaturesymbol(s) may be utilized by a station to transfer additionalinformation to an AP in order to facilitate scheduling of a UL soundingprotocol by the AP. The additional information may include buffer statusinformation, power saving status of the station, etc.

In an aspect, the information contained in the Signature field may beinformation not related to a channel between the AP and the station. Thechannel-related information can be measured from the HE-LTF field(s),but the other information may be communicated by the stations to the AP.Inclusion of the information in the Signature field may reduce overhead,such as relative to a case in which another procedure (e.g., bufferstatus polling) is utilized to collect the information. In an aspect, anNDP trigger frame may include an indication regarding which UL MU NDPformat is used (e.g., the UL MU NDP format with or without the Signaturefield). The NDP trigger frame can include multiple STA-specificinformation (e.g., multiple STA Info fields), which may contain, forinstance, resource indices (e.g., associated with frequency, time,spatial stream, etc.) for signature multiplexing.

In one or more implementations, a pre-acquisition session may beutilized to facilitate an uplink sounding protocol. The pre-acquisitionsession may allow each station, which is a beamformer in the uplinksounding protocol, to initiate a sounding frame sequence, such as shownin FIG. 10 . In an aspect, each beamformer (STA) does not haveinformation about other beamformers (STAs) that may be known to thebeamformee (AP). Therefore, for a UL sounding protocol, each station mayutilize a pre-acquisition session to facilitate successful initiation ofuplink sounding.

In some aspects, the beamformee (AP) may obtain information from thebeamformers (STAs) prior to the UL sounding protocol to facilitate theUL sounding protocol. In this regard, the beamformee may utilize theinformation (e.g., preferred subband information, buffer statusinformation) from the beamformers to determine resources to allocate tothe beamformers.

The information for the pre-acquisition session can be in one or more ofthe following:

-   -   Informed during association (e.g., if the information is        static);    -   Included (e.g., piggy-backed) in UL transmission prior to the UL        sounding protocol;    -   Included in UL request frames (e.g., 1642);    -   Included (e.g., piggy-backed) in an NDP frame. In an aspect, the        NDP frame may include a small payload (e.g., a small HE-DATA        field). In an aspect, the NDP frame may include a Signature        field that can contain the information for the pre-association        session

In one or more aspects, UL sounding may be utilized when a stationrequests UL transmission but does not have sufficient information aboutthe uplink channel. In an aspect, the station can include a soundingrequest in a UL request frame (e.g., 1642). Moreover, in an aspect, thestation can include with the sounding request the number of antennas forbeamforming. In VHT-based sounding protocols, a beamformee may determinea subcarrier group Ng to be used in a beamforming feedback matrix V.Depending on the subcarrier group Ng and bandwidth, subcarrier tones forthe feedback are provided in the IEEE 802.11ac specification:

-   -   A subcarrier group excludes pilot positions and direct        current (DC) positions, while high throughput (HT) can send a        CSI feedback in all data and pilot positions;    -   In the same subcarrier group Ng, the MU exclusive beamforming        report ΔSNR has different subcarrier mapping from the        beamforming report (e.g., compressed beamforming report).

In an aspect, in HE OFDMA transmission, pilot tone positions in thefrequency domain can be different depending on subblock configuration.FIGS. 29, 30, and 31 illustrate examples of numbers of pilots in a 20MHz, 40 MHz, and 80 MHz channel bandwidth numerology, respectively. Thenumerology provides different manners by which to allocate resources forthe channel bandwidth into individual resource units. For example, inFIG. 29 , in a 20 MHz channel bandwidth, there may be 18, 10, or 8pilots. In FIG. 30 , in a 40 MHz channel bandwidth, there may be 36, 20,or 16 pilots. In FIG. 31 , in an 80 MHz channel bandwidth, there may be72, 40, 32, or 16 pilots.

In an aspect, for a given bandwidth (e.g., channel bandwidth), abeamformer may transmit an HE-LTF sequence in every tone position,including pilot tone positions, and each beamformee may determinesubcarrier tones (e.g., data tone positions excluding pilot tonepositions) for which to send feedback depending on a preferred subbandsize.

After sending an NDP frame with an HE-LTF sequence for the whole band(e.g., every tone position including pilot tone positions), thebeamformer may receive feedback reports that include steering matrices.The feedback reports may include an indication of the reporting tonepositions, excluding pilot tone positions, utilized in generating thefeedback reports. After receiving an NDP frame, each beamformee maydecide which subband configuration for feedback is used in a givenbandwidth, calculate feedback matrices, and send an indication to allowthe beamformer to know which tones are used for feedback.

The indication may be implemented as shown in FIGS. 29-31 . In FIG. 29 ,for 20 MHz, the 26-tone basis (the first row) and the 52-tone basis (thesecond row) have the same number of pilots (e.g., 18 pilots). In anaspect, the positions of the pilots may be the same for the 26-tonebasis and 52-tone basis. Therefore, the same indication state (e.g.,state 0) can be shared for both. The 106-tone basis (e.g., associatedwith 10 pilots) and 242-tone basis (e.g., associated with 8 pilots) mayhave other indicate states (e.g., state 1 and state 2, respectively).

In FIG. 30 , for 40 MHz, the 242-tone basis (the fourth row) and484-tone basis (the fifth row) can share the same state (e.g., state 2)since the number of pilots (e.g., 16 pilots) is the same. In FIG. 31 ,for 80 MHz, the first and second rows (e.g., associated with 72 pilotseach), and the fourth and the fifth rows (e.g., associated with 32pilots each) can share their states similarly (e.g., state 0 and state2, respectively).

Although the foregoing description generally provides examples of UL MUsounding protocols, the UL MU sounding protocols may also be applied inthe single user case (e.g., one beamformer and one beamformee).Furthermore, the UL MU sounding protocols may involve fewer or morebeamformers than explicitly described in the foregoing descriptionand/or explicitly depicted in the figures. The horizontal dimension inFIGS. 7, 10-13, and 15-26 represents the time dimension. In someaspects, a time interval between any two frames in the foregoingdescription may be an SIFS, PIFS, or any other time interval (e.g.,represented as xIFS).

The subject disclosure may be utilized in connection with“802.11ac-2013— IEEE Standard for Information technology—Telecommunications and information exchange between systems-Local andmetropolitan area networks— Specific requirements—Part 11: Wireless LANMedium Access Control (MAC) and Physical Layer (PHY)Specifications-Amendment 4: Enhancements for Very High Throughput forOperation in Bands below 6 GHz,” published Dec. 18, 2013 (IEEEStandard), which is incorporated herein by reference in its entirety andincludes, for example, IEEE Standard's Tables 8-53d, 8-53e, 853g, 8-53h,and 8-53j, which are referenced above in this disclosure.

It should be noted that like reference numerals may designate likeelements. These components with the same reference numerals have certaincharacteristics that are the same, but as different figures illustratedifferent examples, the same reference numeral does not indicate that acomponent with the same reference numeral has the exact samecharacteristics. While the same reference numerals are used for certaincomponents, examples of differences with respect to a component aredescribed throughout this disclosure.

The embodiments provided herein have been described with reference to awireless LAN system; however, it should be understood that thesesolutions are also applicable to other network environments, such ascellular telecommunication networks, wired networks, etc.

An embodiment of the present disclosure may be an article of manufacturein which a non-transitory machine-readable medium (such asmicroelectronic memory) has stored thereon instructions which programone or more data processing components (generically referred to here asa “processor” or “processing unit”) to perform the operations describedherein. In other embodiments, some of these operations may be performedby specific hardware components that contain hardwired logic (e.g.,dedicated digital filter blocks and state machines). Those operationsmay alternatively be performed by any combination of programmed dataprocessing components and fixed hardwired circuit components.

In some cases, an embodiment of the present disclosure may be anapparatus (e.g., an AP STA, a non-AP STA, or another network orcomputing device) that includes one or more hardware and software logicstructure for performing one or more of the operations described herein.For example, as described above, the apparatus may include a memoryunit, which stores instructions that may be executed by a hardwareprocessor installed in the apparatus. The apparatus may also include oneor more other hardware or software elements, including a networkinterface, a display device, etc.

FIGS. 32A, 32B and 32C illustrate flow charts of examples of methods forfacilitating wireless communication. For explanatory and illustrationpurposes, the example processes 3210, 3220 and 3230 may be performed bythe wireless communication devices 111-115 of FIG. 1 and theircomponents such as a baseband processor 210, a MAC processor 211, a MACsoftware processing unit 212, a MAC hardware processing unit 213, a PHYprocessor 215, a transmitting signal processing unit 280 and/or areceiving signal processing unit 290; however, the example processes3210, 3220 and 3230 are not limited to the wireless communicationdevices 111-115 of FIG. 1 or their components, and the example processes3210, 3220 and 3230 may be performed by some of the devices shown inFIG. 1 , or other devices or components. Further for explanatory andillustration purposes, the blocks of the example processes 3210, 3220and 3230 are described herein as occurring in serial or linearly.However, multiple blocks of the example processes 3210, 3220 and 3230may occur in parallel. In addition, the blocks of the example processes3210, 3220 and 3230 need not be performed in the order shown and/or oneor more of the blocks/actions of the example processes 3210, 3220 and3230 need not be performed.

Various examples of aspects of the disclosure are described below asclauses for convenience. These are provided as examples, and do notlimit the subject technology. As an example, some of the clausesdescribed below are illustrated in FIGS. 32A, 32B and 32C.

Clause A. A station for facilitating communication in a wireless networkfor multiuser transmission, the station comprising: one or morememories; and one or more processors coupled to the one or morememories, the one or more processors configured to cause: receiving afirst frame from an access point; transmitting a second frame inresponse to the first frame; receiving a third frame, wherein the thirdframe comprises a first beamforming report, and the first beamformingreport is based on the second frame; and generating a beamforming matrixbased at least on the third frame.

Clause B. An access point for facilitating communication in a wirelessnetwork for multi-user transmission, the access point comprising: one ormore memories; and one or more processors coupled to the one or morememories, the one or more processors configured to cause: transmitting afirst frame to one or more stations; receiving a second frame from afirst station of the one or more stations; generating a firstbeamforming report based on the second frame; and transmitting a thirdframe, wherein the third frame comprises the first beamforming report.

Clause C. A computer-implemented method of facilitating communication ina wireless network for multi-user transmission, the method comprising:receiving a first frame from an access point; transmitting a secondframe in response to the first frame; receiving a third frame from theaccess point, wherein the third frame comprises a first beamformingreport, and wherein the first beamforming report is based on one or morehigh efficiency long training field (HE-LTF) symbols of the secondframe; and generating a beamforming matrix based at least on the thirdframe.

In one or more aspects, additional clauses are described below.

A method comprising one or more methods or operations described herein.

An apparatus or a station comprising one or more memories (e.g., 240,one or more internal, external or remote memories, or one or moreregisters) and one or more processors (e.g., 210) coupled to the one ormore memories, the one or more processors configured to cause theapparatus to perform one or more methods or operations described herein.

An apparatus or a station comprising one or more memories (e.g., 240,one or more internal, external or remote memories, or one or moreregisters) and one or more processors (e.g., 210 or one or moreportions), wherein the one or more memories store instructions that,when executed by the one or more processors, cause the one or moreprocessors to perform one or more methods or operations describedherein.

An apparatus or a station comprising means (e.g., 210) adapted forperforming one or more methods or operations described herein.

A computer-readable storage medium (e.g., 240, one or more internal,external or remote memories, or one or more registers) comprisinginstructions stored therein, the instructions comprising code forperforming one or more methods or operations described herein.

A computer-readable storage medium (e.g., 240, one or more internal,external or remote memories, or one or more registers) storinginstructions that, when executed by one or more processors (e.g., 210 orone or more portions), cause the one or more processors to perform oneor more methods or operations described herein.

In one aspect, a method may be an operation, an instruction, or afunction and vice versa. In one aspect, a clause may be amended toinclude some or all of the words (e.g., instructions, operations,functions, or components) recited in other one or more clauses, one ormore sentences, one or more phrases, one or more paragraphs, and/or oneor more claims.

To illustrate the interchangeability of hardware and software, itemssuch as the various illustrative blocks, modules, components, methods,operations, instructions, and algorithms have been described generallyin terms of their functionality. Whether such functionality isimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.Skilled artisans may implement the described functionality in varyingways for each particular application.

A reference to an element in the singular is not intended to mean oneand only one unless specifically so stated, but rather one or more. Forexample, “a” module may refer to one or more modules. An elementproceeded by “a,” “an,” “the,” or “said” does not, without furtherconstraints, preclude the existence of additional same elements.

Headings and subheadings, if any, are used for convenience only and donot limit the invention. The word exemplary is used to mean serving asan example or illustration. To the extent that the term include, have,or the like is used, such term is intended to be inclusive in a mannersimilar to the term comprise as comprise is interpreted when employed asa transitional word in a claim. Relational terms such as first andsecond and the like may be used to distinguish one entity or action fromanother without necessarily requmng or implying any actual suchrelationship or order between such entities or actions.

Phrases such as an aspect, the aspect, another aspect, some aspects, oneor more aspects, an implementation, the implementation, anotherimplementation, some implementations, one or more implementations, anembodiment, the embodiment, another embodiment, some embodiments, one ormore embodiments, a configuration, the configuration, anotherconfiguration, some configurations, one or more configurations, thesubject technology, the disclosure, the present disclosure, othervariations thereof and alike are for convenience and do not imply that adisclosure relating to such phrase(s) is essential to the subjecttechnology or that such disclosure applies to all configurations of thesubject technology. A disclosure relating to such phrase(s) may apply toall configurations, or one or more configurations. A disclosure relatingto such phrase(s) may provide one or more examples. A phrase such as anaspect or some aspects may refer to one or more aspects and vice versa,and this applies similarly to other foregoing phrases.

A phrase “at least one of” preceding a series of items, with the terms“and” or “or” to separate any of the items, modifies the list as awhole, rather than each member of the list. The phrase “at least one of”does not require selection of at least one item; rather, the phraseallows a meaning that includes at least one of anyone of the items,and/or at least one of any combination of the items, and/or at least oneof each of the items. By way of example, each of the phrases “at leastone of A, B, and C” or “at least one of A, B, or C” refers to only A,only B, or only C; any combination of A, B, and C; and/or at least oneof each of A, B, And C.

It is understood that the specific order or hierarchy of steps,operations, or processes disclosed is an illustration of exemplaryapproaches. Unless explicitly stated otherwise, it is understood thatthe specific order or hierarchy of steps, operations, or processes maybe performed in different order. Some of the steps, operations, orprocesses may be performed simultaneously. The accompanying methodclaims, if any, present elements of the various steps, operations orprocesses in a sample order, and are not meant to be limited to thespecific order or hierarchy presented. These may be performed in serial,linearly, in parallel or in different order. It should be understoodthat the described instructions, operations, and systems can generallybe integrated together in a single software/hardware product or packagedinto multiple software/hardware products.

The disclosure is provided to enable any person skilled in the art topractice the various aspects described herein. In some instances,well-known structures and components are shown in block diagram form inorder to avoid obscuring the concepts of the subject technology. Thedisclosure provides various examples of the subject technology, and thesubject technology is not limited to these examples. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the principles described herein may be applied to otheraspects.

All structural and functional equivalents to the elements of the variousaspects described throughout the disclosure that are known or later cometo be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. § 112, sixth paragraph, unless theelement is expressly recited using a phrase means for or, in the case ofa method claim, the element is recited using the phrase step for.

The title, background, brief description of the drawings, abstract, anddrawings are hereby incorporated into the disclosure and are provided asillustrative examples of the disclosure, not as restrictivedescriptions. It is submitted with the understanding that they will notbe used to limit the scope or meaning of the claims. In addition, in thedetailed description, it can be seen that the description providesillustrative examples and the various features are grouped together invarious implementations for the purpose of streamlining the disclosure.The method of disclosure is not to be interpreted as reflecting anintention that the claimed subject matter requires more features thanare expressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed configuration or operation. The following claims arehereby incorporated into the detailed description, with each claimstanding on its own as a separately claimed subject matter.

The claims are not intended to be limited to the aspects describedherein, but are to be accorded the full scope consistent with thelanguage claims and to encompass all legal equivalents. Notwithstanding,none of the claims are intended to embrace subject matter that fails tosatisfy the requirements of the applicable patent law, nor should theybe interpreted in such a way.

What is claimed is:
 1. An access point operating in a wireless network,the access point comprising: one or more memories; and a processorcoupled to the one or more memories, wherein the one or more memoriesinclude instructions, which when executed by the processor cause theaccess point to: transmit a first frame to a plurality of stations inthe wireless network, wherein the first frame indicates to the pluralityof stations to each transmit a null data packet frame to the accesspoint; receive the null data packet frames from the plurality ofstations; after an interframe space period following the first frame,generate beamforming information based on the null data packet frames;and transmit the beamforming information to the plurality of stations.2. The access point of claim 1, wherein the first frame includesresource allocation information for the plurality of stations thatparticipate in an UL OFDMA transmission.
 3. The access point of claim 1,wherein the first frame is a trigger frame.
 4. The access point of claim1, wherein the beamforming information describes a wireless channelbetween the access point and the plurality of stations.
 5. The accesspoint of claim 1, wherein subsequent multi-user downlink transmissionsuse the beamforming information.
 6. The access point of claim 1, whereinthe first frame indicates a number of long-training symbols to beincluded in the plurality of the null data packet frames.
 7. The accesspoint of claim 6, wherein the number of long-training symbols is equalfor all null data packet frames and is set to a maximum rank value.
 8. Afirst station operating in a wireless network, the first stationcomprising: one or more memories; and a processor coupled to the one ormore memories, wherein the one or more memories include instructions,which when executed by the processor, cause the first station to:receive a trigger frame from an access point that triggers a soundingsequence from a set of stations in the wireless network; transmit afirst null data packet frame to the access point as part of a firstmulti-user uplink transmission, wherein the first multi-user uplinktransmission involves the first station and the other stations withinthe set or stations; and receive a multi-user downlink transmission fromthe access point based on the first multi-user uplink transmission. 9.The first station of claim 8, wherein the multi-user downlinktransmission includes first beamforming information describing a channelbetween the first station and the access point and second beamforminginformation describing the channels between the remaining stations ofthe set of stations and the access point.
 10. The first station of claim9, wherein the one or more memories include further instructions, whichwhen executed by the processor, cause the first station to: transmitdata to the access point as part of a second multi-user uplinktransmission, wherein the second multi-user uplink transmission is abeamformed transmission that is configured according to the firstbeamforming information.
 11. The first station of claim 8, wherein thetrigger frame indicates a number of long training symbols to include innull data packet frames included in the first multi-user uplinktransmission.
 12. The first station of claim 11, wherein a long-trainingsequence is used for the long training symbols and is spread acrosstones of the long training symbols, including pilot tones; and whereinthe first beamforming information and second beamforming information isgenerated based on the long training symbols and indicates which tonesof the long training symbols were used for generating the firstbeamforming information and the second beamforming information.
 13. Thefirst station of claim 8, wherein the multi-user downlink transmissionis a beamformed transmission that is configured according to beamforminginformation generated by the access point using the first null datapacket frame and each of null data packet frames transmitted by otherstations within the set of wireless stations.
 14. The first station ofclaim 8, wherein the trigger frame includes an indication that wirelessstations within the set of stations are to transmit a null data packetframe to the access point.
 15. The first station of claim 14, whereinthe trigger frame indicates a length of the first multi-user uplinktransmission and the length of the first multi-user uplink transmissionis set to indicate that the first station is to transmit a null datapacket frame to the access point.
 16. The first station of claim 8,wherein the trigger frame includes first station specific informationthat indicates information for the first station to perform sounding;and wherein the trigger frame includes second station specificinformation and common information that further includes informationthat indicates information for both the first station and other stationswithin the set of stations to perform sounding.
 17. The first station ofclaim 16, wherein the first station specific information includes anidentifier of the first station and indicates a number of spatialstreams for the first station in the first multi-user uplinktransmission; wherein the second station specific information includesidentifiers of the other stations within the set of wireless stationsand indicates a number of spatial streams for the other stations withinthe set of wireless stations in the first multi-user uplinktransmission; and wherein the common information includes frequencyallocation information for the first station and the other stationswithin the set of wireless stations in the first multi-user uplinktransmission.
 18. The first station of claim 8, wherein the multi-userdownlink transmission includes beamforming information used by the firststation for performing beamforming operations with the access point.